Primary lacrimal sac melanoma: a case report describing the novel use of fine needle aspiration cytology (FNAC) for diagnosis, together with literature review and immunotherapy treatment update.

Primary lacrimal sac melanoma (PLSM) is exceedingly rare and associated with high morbidity and mortality. Unfortunately, PLSM often presents insidiously resulting in delayed detection and poor prognosis. A 69-year-old Black man was suspected of having a lacrimal sac tumour following presentation with a left sided watery eye, bloody tears, and a lacrimal mass. Due to the patient's implantable pacemaker, defibrillator, and high anticoagulation, an ultrasound-guided FNAC was performed instead of incisional biopsy, revealing a PLSM. Diagnosis was confirmed following complete tumour resection with free flap reconstruction and neck dissection. Unfortunately, disease progression ensued despite further neck dissection and three cycles of both pembrolizumab and iplimumab. This is the first description of FNAC to accurately diagnose PLSM and highlights its use as an accurate, rapid, and minimally invasive technique that may allow an earlier screening diagnosis of lacrimal sac tumours. We also discuss the outcome of immunotherapy in recent similar cases.