[Radiotherapy in the treatment of Merkel cell tumors]

Merkel cell carcinomas are very rare (80 cases up to 1986) and very malignant; they have been known for 20 years only as "trabecular carcinomas". They do not rise from neural crests, and therefore are not apudomas, but from a staminal cell of the skin with neuroendocrine evolution. Merkel cell carcinomas must be distinguished from undifferentiated carcinomas of the skin, lymphomas, and oat cell carcinomas. Eight patients (46 to 86 years old) are presented, 4 males and 4 females, with 1 gluteal (the younger female patient), 3 head and 4 limb localizations of Merkel cell carcinoma. Radiotherapy was carried out after surgery in 7 patients and after biopsy in 1; local recurrences were already present in 3 cases, and lymph node metastases in 5; tumor doses were 36-65 Gy, administered with different techniques, i.e. roentgen therapy, telecobalt therapy, 192Ir curietherapy. Chemotherapy was used in 2 metastatic patients only. Four patients are alive and free of disease and 4 are dead; 3 of the living patients have been followed 3-26 months. The high risk of radiation damage (1 necrosis, 2 giant edemas, 1 severe fibrosis) recommends that large fields and high single and/or total radiation doses be avoided. In conclusion, surgery is diagnostic but not curative on account of the high risk of recurrence; radiotherapy is important because Merkel cell carcinomas are very radiosensitive. Due to easy lymphatic spread of this type of cancer, radiotherapy must include the regional lymph nodes (dose: 40-50 Gy). The role of chemotherapy is still to be assessed but many antiblastic drugs are effective.