A rare case of clear cell Hidradenocarcinoma presenting with recurrent pleural and cardiac effusion.

Clear cell hidradenocarcinoma (HAC) is a rare and aggressive malignant tumour originating from eccrine sweat glands, accounting for only 0.001% of all tumours. HAC primarily occurs in the head and neck region, with a high propensity for local recurrence and distant metastases. This case report details the unusual presentation of a 66-year-old male with a history of myocardial infarction, hypertension and a significant smoking history, who presented with abdominal pain and progressive shortness of breath. Diagnostic imaging revealed pleural and pericardial effusion and initial workup, including biopsies from pleura, skin and lymph nodes, was inconclusive. Subsequent histopathological examination suggested a diagnosis of HAC with metastases to the pleura, pericardium, lymph nodes, bones and subcutaneous tissues. Despite aggressive diagnostic efforts, the patient succumbed to the disease before chemotherapy could be initiated. This case underscores the diagnostic challenges of HAC, particularly with its atypical presentation and rare metastatic sites, such as the pleura and pericardium. The report emphasises the need for awareness of this rare malignancy and its potential for rapid, fatal progression.