Trisomy 7 in keratoacanthoma and squamous cell carcinoma detected by fluorescence in‐situ hybridization

Keratoacanthoma (KA) is generally considered to be a clinically and histologically distinct entity, but it often remains difficult to separate from well‐differentiated squamous cell carcinoma (WDSCC). Recently, trisomy 7 has been identified in squamous cell carcinoma of the skin. In this study, we examined classical KA (n=6), WDSCC (n=7) and squamous cell carcinoma with KA‐like features (SCC‐KA) (n=8) for trisomy 7 by fluorescence in‐situ hybridization (FISH) to determine if this chromosomal abnormality is unique to squamous lesions diagnosed as WDSCC, or shared by both KA and SCC. In addition, the pertinent clinical‐histopathologic findings were summarized. Trisomy 7 was identified in one KA, one SCC‐KA and two WDSCC. This study demonstrates that there is a chromosomal abnormality shared by KA and SCC, providing further evidence that KA is most likely a form of SCC. Further studies are required to determine if trisomy 7 in these lesions is of prognostic significance.