Hamartin and tuberin immunohistochemical expression in cutaneous fibroepithelial polyps

Background:  Hamartin and tuberin are inactivating tumor suppressor proteins implicated in the development of gastrointestinal polyps and sporadic and tuberous sclerosis-associated cutaneous angiofibromas. The pattern of expression of these peptides has not been studied in fibroepithelial polyps (FEPs). Design:  The specific aim of the study was to evaluate the immunohistochemical expression of tuberin and hamartin within the epithelium and dermal fibrocytes of 20 cutaneous FEPs compared with the epithelium and dermal fibrocytes of normal skin. The diagnoses were confirmed independently by a dermatopathologist, and the pattern of intensity was assessed by the mean labeling intensity (MLI) of cytoplasmic and/or nuclear staining for each antibody. Results:  Hamartin and tuberin antibodies showed moderate staining of the keratinocytes and fibrocytes of normal skin and the keratinocytes within FEPs. Both antibodies showed diminished staining within the fibrocytes of the FEPs. The MLI of hamartin was 44.3 ± 4.4 for keratinocyte nuclei in normal skin and 51.2 ± 3.7 within the polyps. The MLI of tuberin was 42.9 ± 3.6 within the keratinocyte nuclei of the normal skin compared to 39.7 ± 3.0 for the polyps. The MLI for hamartin within the fibrocytes of the normal skin was 78.9 ± 7.1 compared to 21.6 ± 4.2 within the polyps, p = 0.01. The MLI for tuberin within the fibrocytes of normal skin was 70.6 ± 5.0 compared to 47.1 ± 4.7 within the polyps. Conclusion:  The data suggest that down regulation or loss of tuberin and/or hamartin expression may be permissive to fibrocyte proliferation or promote collagen production leading to FEP formation.