Papillary (chromophil) renal cell carcinoma with mucinous secretion.

We investigated the presence of mucin in a series of 20 papillary renal cell carcinomas. Acid mucin was present in three cases (15%), in which basophilic mucin secretion was evident with hematoxylin-eosin. This secretion reacted positively with Mayer's mucicarmine, Alcian blue and high-iron diamine, but was negative for PAS in all the cases, indicating the presence of sulphomucins. We describe two different types of mucin secretion: luminal and intracytoplasmic. The secretion was abundant, diffuse or extensive, luminal in two cases and intracellular in numerous scattered tumor cells in one case. All tumors were < 3 cm in diameter (low grade, stage I). In the three mucin-secreting papillary tumors mentioned above, the immunohistochemical and lectin studies indicate both a proximal and a distal tubular staining pattern. Mucinous secretion in these tumors can be ascribed either to modulation or direct metaplasia of the tumor epithelium. Mucin production, despite its low frequency, can be considered an additional feature of papillary renal cell carcinoma. Thus, the presence of luminal or intracytoplasmic mucin deposition does not exclude papillary renal cell carcinoma from the differential diagnosis in cases of intra- or extrarenal carcinomas.