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Ki-67 and p16 Immunostaining Differentiates Pagetoid Bowen Disease From "Microclonal" Seborrheic Keratosis
Eman Bahrani1, Panitta Sitthinamsuwan2, Timothy H McCalmont1,3
1Department of Dermatology and University of California, San Francisco.
Objectives:
We observed keratoses with "clonal" nests present as numerous tiny collections, in which cells in "pagetoid" array are found, a configuration we termed microclonal seborrheic keratosis (MSK). To better distinguish MSK from pagetoid Bowen disease (PBD), we investigated use of immunohistochemical staining.
Methods:
Biopsy specimens of 26 MSKs, 17 PBDs, and 11 borderline cases were reviewed for histopathology and stained with p53, Ki-67, and p16.
Results:
High expression of Ki-67 and p16 was observed in 12 (80%) of 15 PBDs and in one (4%) of 23 MSKs. Low expression of p16 and high expression of Ki-67 were observed in 16 (70%) of 23 MSKs and in two (13%) of 15 PBDs. Expression of p16 was elevated in 12 (80%) of 15 PBDs and in three (13%) of 23 MSKs (P < .0001).
Conclusions:
We describe a "microclonal" variant of seborrheic keratosis with morphology sometimes challenging to distinguish from PBD. High expression of p16 and Ki-67 or p16 alone favors the diagnosis of PBD over MSK.