PHLDA1, a follicular stem cell marker, differentiates clear-cell/granular-cell trichoblastoma and clear-cell/granular cell basal cell carcinoma: a case-control study, with first description of granular-cell trichoblastoma.

Granular-cell or clear-cell basal cell carcinomas (BCCs), and clear-cell trichoblastomas have rarely been reported in the literature. PHLDA1 is a follicular stem cell marker, the expression of which has been reported to differentiate trichoepithelioma from BCCs. We wondered whether (1) granular-cell trichoblastoma exists and (2) PHLDA1 expression can differentiate a clear- and/or granular-cell trichoblastoma and a BCC. In the records of 2 pathology departments, 12 clear- and/or granular-cell trichoblastomas and BCCs were found. Epidemiological, histopathological, and immunohistochemical data for PHLDA1, Ki67, and AE1-AE3; and cytokeratins 17, 19, 20, and 6hf were collected. Trichoblastomas and clear- and/or granular-cell BCCs occurred in 7 patients (36-62 years; mean: 49) and in 5 patients (63-91 years; mean: 77), respectively. Three granular-cell trichoblastomas were identified. Both granular and clear-cell changes were present in 4 BCCs. The patterns of expression for AE1/AE3, CK17, CK19, CK6hf, and CK20 were not helpful in differentiating trichoblastoma from BCC. PHLDA1 expression was diffusely or partially present in all trichoblastomas (5/5) and absent in BCCs (0/4) (P = 0.008). Granular- and/or clear-cell changes are rare findings in trichoblastoma and BCC. First, we show that granular-cell trichoblastomas do occur. Second, PHLDA1 expression is a useful addition in differentiating trichoblastoma and BCC.