A lack of significantly increased incidence of regression in second primary melanomas does not support an 'immunization effect'

Objective: To compare the incidence of regression in first and second primary melanomas as a possible indication of an 'immunization effect'.

Methods: The first and second primary melanomas of 18 patients were studied histopathologically for signs of regression. At least 1 month elapsed between the removal of the two primary lesions.

Results: Histopathological evidence of regression was found in 7 of the 18 (38.8%) first melanomas and in 8 of the 18 (44.4%) second melanomas [p = non-significant (N.S.)]. Among the nine patients in whom the removal of the second primary melanoma was >6 months after the removal of the first primary melanoma, one (11%) first melanoma and three (33%) second melanomas showed regression, respectively, but this difference did not reach statistical significance. Among the nine patients in whom the removal of the second primary melanoma was ≤ 6 months after the removal of the first primary melanoma, six (67%) first melanoma and five (56%) second melanomas showed regression (p = N.S.).

Conclusions: Our study does not provide evidence for a statistically significant increased rate of regression in second primary melanomas compared to the first primary melanomas, but larger groups of studied cases may be needed.