ANALYSIS OF MICROSATELLITE INSTABILITY AND LOSS OF HETEROZYGOSITY IN KERATOACANTHOMA

We analyzed microsatellite instability (MSI) and loss of heterozygosit y (LOH) at 17 microsatellite markers located on chromosomes 2p, 3p, 5q , 6q, 9p, 9q, 17p and 18q in 19 randomly selected keratoacantomas (KAs ), in one cutaneous lesion that histologically could not unequivocally be differentiated from squamous cell carcinoma, and in one patient wi th multiple KAs of longstanding duration. The goals of our study were to determine whether, in a similar manner to some visceral carcinomas, genomic instability could be detected in KAs and to clarify whether m olecular analysis might be useful to further characterize KA. MSI was observed in 2 of 21 cases (9.5%) at 5 of 17 loci examined. In one pati ent with a solitary KA, the presence of MSI and a family history of vi sceral malignant tumours suggested that the patient might have belonge d to a family with Muir-Torre syndrome. In one other MSI(+) KA, a defi nite differential diagnosis in relation to squamous cell carcinoma cou ld not be established. In addition, one sample displayed LOH at 2 of 1 7 loci analysed whereas in the patient with multiple KAs, LOH at one l ocus was the only alteration found. In conclusion, the low frequency o f MSI and LOH detected in our study suggests that these genetic events are uncommon in KA unless it is associated with a familial disease (e .g. Muir-Torre syndrome) or it has more aggressive histological featur es.