The cost effectiveness of routine histologic examination of excised seborrheic keratotic lesions has been debated. Eads and associates retrospectively studied the diagnostic yield of histologic examination of seborrheic keratoses.

The authors reviewed 577 pathology reports on lesions believed to be seborrheic keratosis. For comparison, 1,592 pathology reports on lesions diagnosed clinically as melanocytic nevi were also reviewed. The specimens had been submitted by community-based dermatologists and other specialists in four midwestern states.

Of the 577 specimens submitted as seborrheic keratoses, 37 (6.4 percent) were histologically interpreted as malignant tumors. Of the 379 lesions with a primary diagnosis of seborrheic keratosis and a differential diagnosis that included only benign tumors, 12 (3.2 percent) were histologically malignant tumors. In contrast, 16 (19.3 percent) of the 84 lesions submitted with a differential diagnosis of malignant tumor were found to be cancer on histologic examination. The physicians who were not dermatologists were three times more likely than dermatologists to mistake a basal cell or squamous cell carcinoma for seborrheic keratosis on the basis of clinical findings.

Seborrheic keratotic lesions with a clinical appearance of irritation or inflammation were more likely to be malignant tumors than were lesions not exhibiting inflammation. Nine (7.8 percent) of the 84 lesions that were described as inflamed or irritated were found to be malignant on histologic examination.

In contrast to the 6.4 percent rate of malignancy in the seborrheic keratotic lesions, 32 (2.0 percent) of the 1,592 lesions thought to be melanocytic nevi were histologically malignant. The rate of malignancy varied and depended on the clinician's concern that the lesion was atypical.

The authors conclude that data from this study indicate that 16 seborrheic keratoses would need to be excised to detect one malignant tumor, and 289 lesions would need to be removed to detect one melanoma. However, if the lesion is inflamed or atypical, then the ratio of benign-to-malignant lesions decreases significantly, to 8:1 for a malignant tumor and 99:1 for a melanoma. The authors note that it was surprising to find that lesions submitted as seborrheic keratoses were more likely to be melanomas than were lesions clinically identified as nevi. The authors believe that their findings support a policy in favor of histologic examination of lesions believed to clinically represent seborrheic keratoses.