[Problems in the special nosological position of keratoacanthoma. Clinical, histological and comparative Feulgen-cytophotometric studies. 3. Classification of keratoacanthomas, therapeutic consequences, conclusions].

Feulgen-cytophotometric examinations of 61 keratoacanthomas of the skin have revealed 3 types differing from each other in their DNA distribution. Keratoacanthomas type I are characterized by a diploid DNA distribution--comparable to epidermis cells. An increasing average DNA content (x) and mean distribution (Sx) compared with diploid cells are, however, conspicuous. Keratoacanthomas type II display DNA peaks in the triploid phase and increasing x and Sx. Keratoacanthomas type III show DNA tumor stem lines in the hypotetraploid, tetraploid and hypertetraploid phases, with x and Sx further increasing. The occurrence of two tumor cell populations of aneuploid localization is noteworthy in part of the keratoacanthomas. Transitional types among the tumors mentioned above are possible. Only type I does not allow cytophotometric demarcation of epidermis cells or tissue lymphocytes based on statistical analysis. The three types of keratoacanthomas can be significantly defined against each other. These cytophotometric findings explain the occurrence of clinical variations of keratoacanthomas with tumor ulceration, increased growth and recidivity. As a rule total excision and careful histological examinations are advisable. The occurrence of paraneoplastic keratoacanthomas and carcinomata disguished as keratoacanthomas is mentioned. Spontaneous healing should not be waited for despite the possible occurrence of benign keratoacanthomas.