Sections show an encapsulated tumour comprising sheets of epithelial cells separated by dense fibrous septa. Tumour cells have pleomorphic ovoid nuclei, cleared chromatin and prominent nucleoli. Tumour nests contain scant lymphocytes and scattered mitoses are seen. Necrosis, marked atypia, intercellular bridges and keratin pearls are not seen. A focus of capsular invasion is present and tumour focally extends to the margin. Lymphovascular and perineural invasion are not seen. In the surrounding fat, there is a lymph node with no evidence of malignancy. Tumour cells show positive staining with CK5/6, p40, c-kit, CD5 and focally with CK7. TTF1 is negative and tumour lacks TdT positive lymphocytes.
Courtesy of Dr Alpha Tsui, pathologist, The Royal Melbourne Hospital.