Abstract

Primary cutaneous signet ring cell/ histiocytoid carcinoma, is a rare and aggressive cutaneous adnexal neoplasm occurring usually on the eyelid and rarely on the axilla with middle aged male predominance. We report a young 27-year-old male presenting with a painless 1.5 cm axillary mass of 1 year duration. The mass was subcutaneous and firm on palpation with erythematous overlying skin. Following excision, pathology showed a diffusely infiltrative malignant cells arranged singly and in cords involving dermis and subcutis. The cells exhibited histiocytoid/signet ring cell morphology with abundant granular cytoplasm and intracytoplasmic vacuoles and enlarged, vesicular and pleomorphic nuclei with conspicuous nucleoli. Multiple atypical mitotic figures and infiltration into adjacent eccrine glandular units surrounded by lymphohistiocytic inflammation was noted.  The neoplastic cells were positive for cytokeratin, CK7, GCDFP, and Her2neu, while negative for CDX2, CK20, TTF1, p63, SOX-10, S100, CD45, chromogranin, ER and PR stains. 

Subsequent targeted next-generation DNA & RNA sequencing (NGS) analysis covering 161 genes using the ONCOMINE Comprehensive assay indicated no significant genomic alterations or copy number changes. In particular, mutations involving PIK3CA, CDH12 and ERBB2 amplification were not identified. The tumor exhibited microsatellite stability and a low tumor mutational burden (TMB). A PET scan revealed intense uptake associated with a 3 cm osteolytic lesion in the right scapula but did not identify any potential malignancy of other primary sites including mammary, gastrointestinal and urinary tract sites. 

Considering the clinical, radiological and histopathological findings, we favor a primary cutaneous signet ring cell/histiocytoid carcinoma.