Primary Malignant Melanoma of the Lacrimal Sac: A Case Report

Background: Primary malignant melanoma of the lacrimal sac is a sporadic and aggressive tumor, accounting for less than 1% of all lacrimal sac neoplasms.Because its symptoms-such as persistent epiphora, medial canthal swelling or bloody dischargeclosely resemble chronic dacryocystitis, diagnosis is often delayed until the disease has reached an advanced stage.Radiological imaging, particularly MRI and CT, plays a pivotal role in early detection, while definitive diagnosis relies on histopathology and immunohistochemistry. Recent advances in immunotherapy have expanded therapeutic options for mucosal melanomas in anatomically complex sites such as the lacrimal drainage system.Case presentation: A 60-year-old man presented with progressive tearing and swelling at the left medial canthus, accompanied by intermittent blood-stained discharge for three months.Physical examination revealed a firm, non-mobile mass over the lacrimal sac without cutaneous ulceration.CT and MRI demonstrated a well-defined lesion within the left nasolacrimal canal, showing T1 hyperintensity and T2 hypointensity suggestive of a pigmented neoplasm.Histopathological examination confirmed malignant melanoma with immunopositivity for HMB-45, Melan-A and S-100.PET-CT revealed distant metastases at diagnosis.The patient received systemic immunotherapy with pembrolizumab (200 mg every three weeks), achieving partial remission before progression at 18 months.He was subsequently placed on palliative care.Discussion: This case underscores the diagnostic challenges of lacrimal sac melanoma, given its rarity and nonspecific presentation.Multimodal imaging and early biopsy are crucial to distinguish it from chronic inflammatory disease.Immunotherapy, particularly PD-1 blockade, represents a promising alternative to extensive surgery in metastatic or unresectable cases.Conclusion: Prompt recognition and multidisciplinary management are essential for improving outcomes in this aggressive malignancy.Lifelong surveillance remains mandatory due to the high risk of recurrence and metastasis.