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. Bergman R, Zoller L, Mayer E, Itzhak OB. A lack of significantly increased incidence of regression in second primary melanomas does not support an ‘immunization effect’.