From hidroacanthoma simplex to poroid hidradenoma: clinicopathologic and immunohistochemic study of poroid neoplasms and reappraisal of their histogenesis.

BACKGROUND: Poroid neoplasms comprise classic poroma (P), hidroacanthoma simplex (HS), dermal duct tumor (DDT), and poroid hidradenoma (PH). The 3 latter are rarely reported. Poroid cells in P have recently been identified as keratinocytes of the lowermost acrosyringium and the sweat duct ridge.
OBJECTIVES: To investigate a large cohort of poroid neoplasms to better define the clinical and pathologic aspects of HS, DDT, and PH. To analyze the expression of discriminatory keratins in all 4 poroid neoplasms.
METHODS: 202 P, 11 HS, 17 DDT, 31 PH, and 5 composite tumors were examined under light microscopy, and 11, 9, 10, 15, and 2, respectively, by immunohistochemistry using anti-keratin antibodies, in particular, anti-K77, specific for luminal cells of the eccrine dermal sweat duct, and Ki-67 antibody.
RESULTS: HS appeared later in life (66.6 years old) than P, DDT, and PH. Whereas P, DDT, and PH displayed unspecific clinical aspects, HS had most frequently the aspect of a large seborrheic keratosis with well-defined borders. HS, DDT, and PH were absent on palms and soles, but were found on the trunk, the lower limbs, and the upper limbs. Similar pathologic features were observed in all tumors, that is, a majority of poroid cells expressing K14, islands of K10-positive and K77-negative large cells. K77 expression was limited to luminal cells of intact ductal structures within the tumors.
CONCLUSIONS: Our data demonstrate the common histogenesis of the 4 poroid neoplasms, which seem to derive from the basal keratinocytes of the sweat duct ridge and the lower acrosyringium. The variable length of the sweat duct ridge may account for the variety of poroid neoplasms, according to the site of tumor induction along this structure.