CoM is a rare ocular malignancy, representing 2%–5% of all ocular tumours and 5%–7% of all ocular melanomas. Its incidence rate in the individuals of European descent adult population is 0.3–0.8 per million [5, 10, 12]. Compared to individuals of European descent, black people and Asians have a significantly lower incidence of conjunctival melanoma (CoM) [18]. Several studies have shown that the CoM incidence rate is rising [5, 18]. The incidence of the condition increases with age, with the average age at clinical presentation ranging from 55 to 65 years, and a mean age of 57.4 years at histopathological diagnosis [21]. It is exceedingly rare in the population under the age of 20 [5, 21, 34, 47]. While no definitive gender predilection has been identified, some studies have shown that males tend to be younger than females when diagnosing primary tumours [5, 21, 47].

CoM can arise de novo or from pre-existing melanocytic lesions, most commonly conjunctival melanocytic intraepithelial lesions (C-MIL), which account for approximately 70% of cases [2, 57, 58]. Previously termed conjunctival melanocytic intraepithelial neoplasia (C-MIN) or primary acquired melanosis (PAM) with atypia, C-MIL represents a preinvasive spectrum ranging from melanocytic hyperplasia to melanoma in situ [59]. In 2018, the fourth edition of the WHO Classification of Ocular Tumours introduced a simplified grading system that categorized C-MIL as low-grade (corresponding PAM with mild or no atypia or C-MIN grades 1–2), high-grade (corresponding PAM with moderate to severe atypia or C-MIN grades 3–5), and melanoma in situ (PAM with severe atypia involving >75% of the epithelial thickness or C-MIN >5). This system was validated in 2021, demonstrating comparable predictive accuracy across the C-MIL, C-MIN, and PAM classifications for recurrence risk [57].

In 2022, the fifth edition of the classification refined this scheme, acknowledging that the previous low-grade C-MIL category encompassed both neoplastic and non-neoplastic melanocytic proliferations. The current system stratifies C-MIL into low- and high-grade categories based on histopathologic features. Low-grade C-MIL is characterized by predominantly basal melanocytic proliferation with mild cytologic atypia and carries a relatively low risk of progression to invasive melanoma. In contrast, high-grade C-MIL exhibits basal and prominent suprabasal proliferation of atypical melanocytes, marked cytologic atypia and a significantly higher risk of invasive transformation. Notably, melanoma in situ is now included within the high-grade C-MIL category, referring to lesions with near full-thickness epithelial involvement or those that histologically resemble melanoma without evidence of subepithelial invasion [59]. The revised classification, validated in a large international study, showed strong interobserver agreement, high reproducibility, and prognostic value, supporting its use in guiding therapy [58, 59].

Conjunctival melanocytic nevi are common benign proliferations of melanocytes, typically forming in the first decade of life. Histopathologically, the three most common types are junctional nevi, compound nevi, and subepithelial nevi, which may represent different stages of melanocyte maturation and proliferation [60]. Although conjunctival nevi rarely undergo malignant transformation, approximately 2% of cases can develop into melanoma [61]. Nonetheless, about 7% of all CoMs are believed to originate from pre-existing conjunctival nevi [47].

Deep penetrating nevi (DPN), also known as melanocytomas, account for 9.4% of all excised conjunctival nevi. Defined by their distinctive morphology, DPNs exhibit a nested or plexiform growth pattern of primarily epithelioid melanocytes with vesicular nuclei and finely pigmented cytoplasm, often accompanied by melanophages. Immunohistochemical analysis typically shows positivity for the BRAFV600E mutation, with activation of the beta-catenin pathway frequently observed. Clinically, conjunctival DPNs appear as dark brown pigmented lesions with uniform or irregular pigmentation, most commonly found on the bulbar conjunctiva (44%), caruncle (21%), and semilunar fold (21%). Due to their atypical clinical features and growth potential, these lesions are often excised. Accurate recognition of DPN of the conjunctiva is essential to prevent its misdiagnosis as melanoma, given that DPN is a benign lesion [62–65]. Additionally, in 11%–26% of cases, CoMs develop “de novo,” with no precursor lesions being identified [20, 21, 47, 66].

CoMs typically present as asymptomatic raised pigmented plaques, tumours, or macules on the bulbar or tarsal conjunctiva [6]. The most commonly affected sites are the bulbar conjunctiva (56%–79% of cases), the conjunctiva of the fornices and palpebrae (9%–29% of cases), and the caruncle (1%–7% of cases) [66–68]. While these tumours are often pigmented, they can also be non-pigmented or show mixed appearance [47, 67, 68]. Although multiple lesions are uncommon, they have been reported more frequently in cases associated with PAM [47].

Histologically, CoM comprises various cell types, including nevoid, epithelioid and spindle cells. Nevoid cells resemble benign nevi. Epitheloid cells are large with abundant cytoplasm and prominent nucleoli, showing significant pleomorphism and mitotic activity, while spindle cells are elongated with less cytoplasm. Tumor architecture varies, presenting as flat, nodular, or diffuse growths, sometimes with intraepithelial spread. Deeper tissue invasion, such as into the sclera or orbit, indicates advanced disease and a worse prognosis. Although variable, melanin pigmentation is a notable feature, and thus heavily pigmented melanomas are easier to diagnose, while amelanotic melanomas require immunohistochemical (IHC) staining for identification. IHC markers, including S-100 protein, HMB-45, Melan-A, and SOX10, confirm the melanocytic origin of the tumour and distinguish it from other pigmented lesions [20, 26, 32].

Exposure to ultraviolet (UV) radiation is a well-established risk factor for CM. However, its role in the development of CoM remains a topic of debate [6]. Epidemiological studies have suggested a correlation between the increasing incidence of CoM and decreasing latitude, indicating that sun exposure may play a role in its development [25, 26]. Despite these findings, the exact impact of UV radiation on CoM is not yet fully understood.

Several studies have documented the presence of a UV signature in DNA damage from CoM samples [26, 29, 30]. A recent study revealed that 86% of bulbar CoMs exposed to sunlight exhibited a high (>70%) mutational load of C > T changes, indicative of UV-induced DNA damage. CoMs in sun-exposed bulbar areas more frequently harbour BRAF mutations than those from non-exposed sites [20]. BRAF mutations are found in about one-third of CoMs, with the V600E mutation being the most prevalent, present in approximately 80% of cases [20, 26, 32]. These mutations are associated with intermittent sun exposure, suggesting a potential link between UV exposure and CoM [33]. However, other studies have found no significant difference in the expression of oncology-related genes between melanomas from sun-exposed and non-exposed areas [69].

Several conditions are associated with an increased risk of CM, including familial atypical multiple mole melanoma (FAMMM) syndromes and BAP-1 tumour predisposition syndrome [70]. However, up to the present time, no similar conditions have been identified as risk factors for CoM.

Most genetic studies on CoM primarily analyse somatic mutations and structural variations in primary tumour samples. This focus is due to the sporadic nature of CoMs, employing targeted or comprehensive methods. CoM exhibits a unique genetic profile that overlaps significantly with mucosal and cutaneous melanomas, but less with UM. Key mutations in the CoM landscape include alterations in genes such as BRAF, NRAS, KIT, NF1, and ATRX, which often coexist with UM-associated mutations like BAP1, SF3B1, and GNAQ/11. These genetic alterations are correlated with advanced disease, an increased risk of metastasis, and poorer prognosis, indicating a need for proactive treatment approaches and rigorous monitoring for affected patients [71].

Two highly complex and interconnected biological pathways commonly deregulated in CoMs are:

1. Mitogen-Activated Protein Kinase (MAPK) Pathway: Also known as the RAS/RAF/MEK/ERK pathway, it regulates gene expression by converting numerous genes into RNA, sending growth signals to the nucleus, and controlling multiple cellular activities such as differentiation, proliferation, and survival [45].

The presence of a “UV mutational signature” characterised by CC > TT substitutions and a predominance of C > T substitutions at dipyrimidine sites indicates DNA damage from UV light. This signature often corresponds with a higher tumour mutational burden (TMB), reflecting differences between epithelium-associated melanomas (such as cutaneous and mucosal melanomas) and non-epithelium-associated melanomas (like uveal and leptomeningeal melanomas) [72]. Mucosal melanomas, including CoM, typically show a lower TMB and fewer UV signals, despite being more common in sun-protected areas. Ocular melanomas that arise in varying sunlight exposure conditions demonstrate similar UV signature presence and TMB levels, with CoMs often having higher TMB levels linked to UV exposure [73].

The gene BRAF, which encodes a serine/threonine kinase that activates the MAPK pathway by triggering MEK, is situated on chromosome 7 at the q34 region. Certain oncogenic mutations in BRAF cause the BRAF proteins to become activated on their own, permanently activating MEK1/2 and ERK1/2 via the MAPK pathway and promoting the formation of tumours [45]. Roughly one-third of CoMs have been reported to contain BRAF mutations [32]. While mutations can arise at other codons of the BRAF gene, the majority of documented mutations have occurred at codon 600, where valine is replaced by glutamic acid (p.V600E; 80%–90%), lysine (p.V600K; 9%–20%), or infrequently by another amino acid. These features resemble CMs, although posterior UMs typically do not have BRAF mutations [74, 75]. BRAF-mutated CoMs occur more frequently on sun-exposed/bulbar conjunctiva, suggesting UV exposure as a potential risk factor [20, 76].

Situated on chromosome 1p13, NRAS belongs to the same family as other RAS genes. It codes for a GTPase incorporated into the MAPK cascade and upstream of BRAF. It may also be the first step in the PI3K/AKT/mTOR pathway [56]. While NRAS mutations are uncommon in posterior UMs, they were found in 20% of the CoMs, similar to CM [74]. Point mutations in the NRAS gene that affect codons 61 (Q61R and Q61K are the most common) or codons 12 or 13 (G12/13) lead to uncontrolled cell division [56]. Conjunctival nevi also show NRAS mutations [77]. A link between NRAS mutations and more aggressive tumour features, including a higher chance of metastasis and death, has been suggested [71, 76]. MEK inhibitors have been studied as single medicines or in conjunction with PI3K/mTOR inhibitors for tumours with NRAS mutations, although data regarding their application in advanced CoM with NRAS mutation is lacking [78].

Chromosome 17q11 contains the NF1 gene, which produces a tumour suppressor protein that prevents RAS and acts as an inhibitory regulator of the PI3K/AKT/mTOR and MAPK pathways. Higher RAS activity is linked to loss-of-function or inactivating NF1 mutations, which lead to excessive signaling. NF1 mutations have been detected in about one-third of CMs, mostly nonsense or frameshift mutations. Although rare, F1 mutations can coexist with NRAS or BRAF mutations in CoMs [71, 76]. There is no known correlation between NF1 mutations and clinicopathological characteristics or prognosis [71, 76]. Like CMs, NF1 mutations seem more common in CoMs linked to a UV signature, indicating potential benefits from immunotherapy for patients with NF1 mutations [9, 31, 48].

Chromosome 4q12 contains the KIT gene, which encodes a receptor tyrosine kinase [RTK] that activates several downstream pathways, including the PI3K/AKT/mTOR and MAPK pathways [56]. BRAF and NRAS mutations are typically absent from CoMs with activating mutations and/or gains in the KIT gene/locus, indicating mutual exclusivity [76]. KIT mutations can coexist with NF1 mutations in CoMs, similar to the way BRAF and NRAS mutations can. KIT mutations are frequently found in non-sun-exposed CMs and sun-protected mucosal melanomas. Although no correlation has been observed between CoM survival and KIT status, c-KIT inhibitors are appropriate targets for KIT-mutated malignancies, although their effectiveness in CoM patients remains unclear [78].

The PTEN gene, located on chromosome 10q23, encodes a tumour suppressor protein that inhibits the AKT/mTOR pathway by negatively regulating PI3K. Loss of PTEN activity, due to mutations, deletions, or decreased expression, leads to increased PI3K activity and excessive PI3K/AKT/mTOR signaling. Like skin melanomas, CoMs may exhibit elevated mTOR pathway activity and decreased or absent PTEN expression. Notably, PTEN expression is generally higher in UMs than in CoMs [9, 79].

The cellular location of PTEN (nuclear versus cytoplasmic) influences its activity, with the nuclear fraction primarily responsible for tumour suppression. CoMs show more prominent nuclear PTEN loss than conjunctival nevi, suggesting a significant role in oncogenesis and malignant transformation. Recent studies have reported inactivating PTEN mutations alongside copy number changes that induce PTEN loss in CoMs. Although PTEN and NRAS mutations typically do not co-occur, they frequently appear with BRAF or KIT mutations [78].

Interestingly, a study linked PTEN loss to CoM pigmentation, indicating that amelanotic tumours exhibited greater nuclear PTEN expression than pigmented tumours. Despite the lack of correlation with other CoM-related characteristics or prognosis/survival thus far, CoMs with PTEN loss may be candidates for targeted treatments using mTOR inhibitors [71].

The TERT gene, located on chromosome 5p15, encodes the catalytic protein subunit of telomerase, a ribonucleoprotein polymerase that maintains telomere length. In normal somatic cells, telomerase expression is suppressed, leading to telomere shortening and eventual cell senescence. However, abnormal telomerase activity can allow cells to become “immortal.”

Like skin melanomas, CoMs typically contain 35%–40% TERT promoter (TERTp) mutations at similar sites [78]. These mutations often exhibit a characteristic UV signature and can co-occur with BRAF or NRAS mutations. TERTp mutations can enhance TERT expression, allowing neoplastic cells to survive indefinitely, although the exact causes of elevated TERT expression in CoMs remain unclear. While conjunctival nevi do not have TERTp mutations, lesions with atypia do, suggesting a link to malignant transformation. Recent findings indicate that TERTp mutations are also present in non-PAM-derived CoMs, warranting further investigation. Unlike CoMs, TERTp mutations are uncommon in posterior UMs, but they have been associated with metastatic development in CoMs, highlighting their prognostic significance [74]. Furthermore, TERTp-mutated cancers may eventually be treated with telomerase and reverse transcriptase inhibitors [9, 80].

The ATRX gene, located on chromosome Xq21, encodes a chromatin remodelling protein essential for homologous recombination and DNA methylation-mediated epigenetic regulation of alternative telomere lengthening (ALT). Inactivating mutations and loss of ATRX protein expression are frequently observed in malignancies utilising the ALT pathway for telomere maintenance, such as mucosal melanomas [81].

ATRX mutations have been identified in approximately 20%–60% of CoM patients, with subsequent validation confirming these mutations in 25% of cases. Functional studies revealed that ATRX-mutated tumours exhibit ALT positivity and loss of ATRX protein expression [71]. ATRX mutations co-occur more frequently with NF1 mutations than NRAS or BRAF mutations. Additionally, ATRX-mutated CoMs often harbour mutations in genes associated with histone modification and epigenetic regulation, such as HDAC, SETD genes, CREBBP, or MLLT6 [9, 48].

ATRX mutations also frequently co-occur with TP53 alterations in CoMs and other mucosal melanomas. While ATRX loss and TERT activation typically demonstrate mutual exclusivity in various cancers, further research is needed to explore their combined genetic changes in CoMs. The early detection of ATRX loss and ALT positivity in both the intraepithelial and invasive components of CoMs suggests their involvement in tumorigenesis. The prognostic relevance of ATRX-mutated CoMs is reflected in their tendency to develop in non-sun-exposed areas and their association with less aggressive behaviour. CoMs with ATRX mutations may also resist anti-telomerase therapy while being vulnerable to PARP inhibitors, indicating potential therapeutic implications [71]. In their study, van Ipenburg et al. report a correlation between TERT promoter mutations and decreased metastasis-free survival in conjunctival melanoma (CoM). The findings indicate that CM with ATRX loss also tends toward poorer outcomes, highlighting that both TERT promoter mutations and ATRX loss are associated with adverse clinical behaviour. The presence of TERT promoter mutations was strongly linked to shorter metastasis-free survival, suggesting a similar risk profile for CM cases exhibiting ATRX loss [82]. Additional genes found in CoM are presented in Table 2.

Furthermore, other mutated genes relevant to CoM pathophysiology have been identified, including CTNNB1, ACSS3, PREX2, APOB, RYR1/2, SYK, NOTCH3, CHEK2, KMT2A/C, ARID2, FAT4, RB1, APC, and members of the MAPK/MAP2K/MAP3K signaling cascades. Their precise roles remain to be clarified and merit further investigation [84].

CoMs also display various chromosomal abnormalities, including.

• Numerical chromosomal abnormalities: Polyploidy or aneuploidy.

Amplifications in regions like 6p21–25, particularly at 6p22’s histone cluster 1 area, suggest the presence of important oncogenic drivers (e.g., BRAF, NRAS, and TERT) while deletions affecting NF1, TP53, and others indicate a complex genetic landscape [25, 31, 70].

Despite the unclear processes underlying recurrent chromosomal aberrations in CoMs, integrative analyses could provide insights. Patterns of CNAs vary with genetic backgrounds, with BRAF/NRAS wild-type tumours showing notable increases [86].

MicroRNAs (miRNAs) play a significant role in CoM pathophysiology by facilitating post-transcriptional gene silencing. Many miRNAs, such as miR-30d, miR-506, miR-509, miR-146, and miR-20b, are elevated in CoM and may serve as therapeutic targets or prognostic indicators. For instance, upregulation of miR-20b is associated with PTEN suppression, and inhibiting miR-506 and miR-509 reduces cell proliferation and invasiveness in CoM [24, 87].

Understanding the interactions of miRNAs, such as miR-146a with NOTCH proteins, emphasises their role in early cancer formation in CM and highlights potential avenues for targeted therapies in CoM management [88, 89].

Key findings from the study by Larsen et al. (2016) identified specific miRNAs distinctly expressed in conjunctival melanoma compared to healthy conjunctival tissue. These miRNAs may help differentiate malignant tissue from normal conjunctiva, aiding in diagnosis. Several miRNAs, such as miR-204 and miR-211, were found to be significantly downregulated in conjunctival melanoma. This downregulation was associated with more aggressive tumour characteristics, suggesting these miRNAs could serve as prognostic biomarkers for assessing the risk of tumour progression. The dysregulated miRNAs are involved in pathways critical for cancer development, including cell proliferation, apoptosis, and immune response modulation. These pathways are essential in understanding the mechanisms behind conjunctival melanoma’s aggressive behaviour [89].

Mikkelsen et al. (2019) identified unique miRNA expression patterns in metastatic conjunctival melanoma, with certain miRNAs overexpressed in metastatic cases compared to non-metastatic samples. Specific miRNAs, such as miR-21 and miR-146b, were notably associated with metastatic behaviour in conjunctival melanoma. These miRNAs may have potential as prognostic biomarkers, helping to identify patients with a higher risk of metastasis. Understanding miRNA involvement in metastasis offers potential therapeutic targets, as manipulating miRNA levels could provide a new approach to slow disease progression and improve patient outcomes in metastatic conjunctival melanoma [13]. Also study by van Ipenburg et al. (2020) identified five miRNAs that were upregulated in conjunctival melanoma compared to nevi, with higher levels of miR-9-5p, miR-196b-5p, and miR-615-3p strongly associated with malignancy. The shared pathway involving these miRNAs, possibly linked to homeobox gene clusters, suggests a role in conjunctival melanoma pathogenesis. Additionally, this miRNA combination may help distinguish benign from malignant lesions, especially when tissue samples or diagnostic methods are limited. However, no miRNAs were identified to predict metastatic potential, underscoring the need for further research in this area [90].

With advancements in RNA sequencing and bioinformatics, circular RNAs (circRNAs), a type of circular non-coding RNA, have emerged as a focal point in cancer research [91]. Numerous circRNAs linked to cancer have been identified by various research teams, highlighting their potential roles in tumour development and progression. In the study of Shang et al. (2019), the authors identified over 9,300 circRNA candidates in conjunctival melanoma tissue compared to adjacent normal tissue. Among these, circMTUS1 was confirmed as a circular RNA upregulated in melanoma tissues and cell lines. Functional assays demonstrated that circMTUS1 supports tumorigenesis both in vitro and in vivo, likely by sequestering hsa-miR-622 and hsa-miR-1208 and influencing pathways associated with cancer. This suggests that circMTUS1 may serve as a novel biomarker for conjunctival melanoma, providing potential diagnostic and therapeutic targets in this field [92].

The preferred treatment for localised CoM involves a comprehensive approach that includes total surgical excision using a “no-touch” technique. This method employs new, clean instruments at every stage of the procedure, reduces the possibility of tumor seeding, and requires excision-wide tumor-free conjunctival margins of 2–4 mm. Supplemental cryotherapy using a “double freeze-thaw” technique is applied to the conjunctival margins, and alcohol corneal epithelialectomy is performed if the tumour extends to the corneal limbus. It is important to preserve the Bowman layer, as it serves as a natural barrier against tumour invasion [6]. Supplemental treatments aim to eliminate any clinically undetectable tumour cells that may remain along the resection margins, thus preventing the spread of viable tumour cells [68]. Surgical excision alone, without adjuvant therapies such as plaque brachytherapy, topical chemotherapy (e.g., mitomycin C), or interferon alpha-2b, is generally discouraged due to the higher risk of local recurrence and increased mortality [21, 45, 68, 99].

Several prospective and retrospective series have confirmed that combining wide local excision and cryotherapy with adjuvant topical chemotherapy or plaque brachytherapy significantly improves outcomes in patients with localized CoM. In a long-term study involving 85 patients, Werschnik and Lommatzsch reported a 10-year tumor-related survival rate of 77.7% and an overall survival rate of 62.5%. Notably, they observed significantly fewer recurrences in patients who received adjunctive treatment, such as irradiation, cryotherapy, or local chemotherapy with mitomycin C (MMC), in addition to surgical excision, compared to excision alone [99]. Similarly, a large nationwide cohort study conducted in the Netherlands, encompassing 194 patients treated between 1950 and 2002, found a local recurrence rate of 58% (median follow-up of 6.8 years) and a regional lymph node metastasis rate of 21%. Outcomes were significantly improved in patients treated with adjuvant brachytherapy compared to those who underwent excision alone or excision with cryotherapy [21]. In a cohort of 150 patients, Shields et al. demonstrated that the absence of adequate adjuvant therapy was associated with a 26% metastasis rate at 10 years and a tumor-related mortality rate of 13% by 8 years [68].

Cryotherapy applied to the surgical margins following excision plays a crucial role in eliminating residual tumor cells, with its mechanism of action involving both direct cytotoxic effects, such as disruption of cellular integrity through intracellular content efflux, and ischemic injury resulting from damage to the local microvasculature [107]. The adjunctive use of cryotherapy has been shown to significantly reduce the risk of tumor recurrence compared to excision alone. Specifically, recurrence rates have been reported at 18% with adjuvant cryotherapy versus 52% with excision alone [108, 109]. These findings underscore the importance of incorporating cryotherapy into the standard surgical management of CoM to improve local disease control and reduce recurrence rates in CoM.

Topical chemotherapeutic agents used as adjuvant therapy for CoM include mitomycin C (MMC) and interferon alpha-2b. MMC, an alkylating agent, is the most commonly used agent and is considered the standard adjuvant therapy in many centers. To reduce the risk of scleral thinning or melting, initiation of therapy is typically delayed for several weeks following surgical excision, allowing for sufficient wound healing. MMC is usually administered at a concentration of 0.04%, four times daily, in treatment cycles lasting one to 3 weeks, separated by 1-week drug-free intervals. Although its efficacy as a primary treatment is limited due to poor penetration through the basement membrane and reaching deeper tissues, MMC effectively eliminate residual superficial tumor cells. Topical application is frequently associated with transient but often severe keratoconjunctivitis, which is self-limiting and occurs in nearly all patients [110–112]. In a phase I trial by Finger et al., adjuvant MMC (0.04% QID for 7 days following excision) resulted in no tumor recurrence over a mean follow-up period of 29 months [106].

Interferon alpha-2b, a naturally occurring cytokine with antiproliferative, immunomodulatory, and pro-apoptotic effects, represents an alternative adjuvant approach. It exerts its antitumor activity by prolonging the cell cycle, enhancing the expression of tumor suppressor genes, and downregulating oncogene expression [113]. Administered topically at a concentration of 1,000,000 IU/mL, four to five times daily for six to 12 weeks, interferon alpha-2b is generally well tolerated and may be particularly beneficial for patients who are intolerant to MMC. However, its role in the treatment of CoM remains fully elucidated, and further prospective studies are needed to establish its efficacy [114, 115].

Radioactive plaque brachytherapy represents a well-tolerated and effective adjuvant modality in the multidisciplinary management of CoM. While CoM exhibits relative radioresistance and plaque brachytherapy is not typically employed as a primary treatment, its adjuvant use offers a distinct advantage by delivering localized radiation to deeper stromal tissues, beyond the reach of topical chemotherapeutic agents. Ruthenium-106 plaques are most frequently utilized, delivering a prescribed dose of 100 Gray to a standardized depth of 2 mm. This targeted approach has demonstrated favorable local control rates, with reported recurrence rates of 19% at 3 years and 21% at 5 years, while preserving visual function and minimizing ocular morbidity [116, 117]. These outcomes support the integration of plaque brachytherapy into the treatment algorithm for select CoM patients, particularly those with high-risk histopathological features or residual deep scleral invasion following surgical excision.

Incisional biopsies should generally be avoided due to the risk of tumour spread and local recurrence [68, 118]. However, they may be considered in cases where total surgical removal of the tumour is not feasible [6]. Orbital exenteration is reserved for patients with extensive CoM involving orbital or intraocular invasion [66]. Sentinel lymph node biopsy (SLNB) is recommended for melanomas larger than 10 mm in diameter, and 2 mm in thickness, with histological ulceration, scleral invasion, or tumors found in areas other than the bulbar conjunctiva [6, 119–123]. It offers an early opportunity for intervention before systemic metastasis occurs and can detect subclinical nodal metastases missed by clinical or ultrasound examination [119, 124]. Typically performed after excision of the primary tumour, SLNB can be important for accurate staging and guiding treatment decisions. A positive SLNB is associated with poorer metastasis-free and disease-specific survival, underscoring its importance for prognosis and identifying high-risk patients for adjuvant therapy [104, 125]. While SLNB offers valuable prognostic information in selected patients with CoM, certain contraindications and technical challenges may limit its broader application. Prior surgeries or radiation in the head and neck may alter lymphatic drainage, impairing SLN localization. Hypersensitivity to radiotracers or dyes, significant comorbidities, and minimal metastatic risk, such as in situ or thin (<1 mm) tumors, further restrict its indication. The periocular region presents unique challenges, including the need for precise tracer injection near critical structures and the risk of technetium leakage, which can be reduced by immediate ocular coverage and contralateral head positioning. Ophthalmic administration and preoperative lymphoscintigraphy improve accuracy while maintaining low radiation exposure. Facial nerve injury during parotid dissection and transient blue staining of ocular tissues highlights the need for specialized surgical expertise. Despite these considerations, SLNB remains a safe and informative procedure when applied within established protocols [5, 98, 104, 121, 126].