Since malignant clear cell
hidradenoma (CCH) is often characterized by only slight and sometimes by absent nuclear
anaplasia, even in
metastases, definitive differentiation from its benign counterpart by light microscopy may be very difficult. Herein, we report the case of a 72-year-old woman suffering from a CCH on the back, which showed local recurrence following incomplete excision. By light microscopy no unequivocal signs of
malignancy were found either in the primary or the recurrent
tumor. However, unusual deep extension to the subcutis with some architectural disorder was seen in the latter. Identification of prospective
malignancy in such cases of borderline histopathological features is one of the main indications for diagnostic
DNA image cytometry (ICM-
DNA). Application of this method to enzymatic cell separation specimens of the recurrence detected marked
DNA-
aneuploidy with a stemline ploidy of 2.60 c and single events up to 6.7 c, whereas a nearly exact diploid
DNA-stemline was found in the primary. We suppose from our results that a prospective malignant CCH with
aneuploid DNA-stemline has developed out of its
DNA-diploid counterpart. The need for total surgical removal of apparently benign clear cell
hidradenomas is further stressed by this observation. Criteria for the diagnosis of
malignancy in CCH are reviewed.