[Malignant melanoma treated with radical chemotherapy, resemblance histology of melanoma to soft tissue sarcomas, case report].

Background: Malignant melanoma is considered to be highly resistant to chemotherapy, radiotherapy, hormonotherapy and standard immunotherapy (interleukin 2, interferon alpha). Radical surgery in the early stages of the disease is still the most efficient method. Since the development of immunotherapy and targeted therapy, the role of palliative chemotherapy for advanced disease may be changing.

Case: A case report regarding 44-year-old woman with extensive tumor of the pectoral wall with contralateral axillary lymphadenopathy is presented. On the basis of imaging methods, histology and immunohistochemistry, the tumor was defined as a sarcoma. Due to PAX7-FKHR fusion gene positivity, rhabdomyosarcoma was the most probable classification. The patient was treated with radical chemotherapy including iphosphamide, vincristine, actinomycin D and doxorubicin with the effect of partial regression of the tumor. This enabled radical surgery of the chest wall tumor. Pathology proved 70% necrosis of the tumor. A contralateral axillary dissection was performed with a finding of two lymph nodes infiltrated with melanoma. The immunohistochemistry markers S100, HMB-45 and Melan A were positive. This resulted in a reclassification of the chest wall tumor to malignant melanoma. The following PET/CT scan was negative. A massive progression of the disease occurred after 5 months. B-RAF mutation leads to a plan of targeted therapy with vemurafenib.

Conclusion: The case demonstrates the limits of the sensitivity and specificity of immunohistochemical markers of melanoma and the ability of this tumor to imitate various tumors including soft tissue sarcomas. A rare -PAX7-FKHR fusion gene positivity considered specific for rhabdomyosarcoma was found. An extraordinary response to radical chemotherapy with surgical resection led to an improvement of the quality of life and to a prolonged survival comparable with the effect of new targeted treatment for malignant melanoma.