The function of different growth factors in the development and progression of malignant tumors and the role of cytotoxic cytokines in the host response generated against neoplasms have been recently studied. Anti-TGF-α and anti-TNF-α monoclonal antibody families have been developed and characterized previously by our laboratory. Libraries of anti-TGF-α and anti-TNF-α monoclonal antibodies were selected for equal immunoreactivity both in native (frozen) and in formaldehyde fixed, paraffin embedded histological sections. No differences were found between native and fixed samples demonstrated in 10 cases in the present prospective study. Retrospective investigation was performed in 35 histopathological specimens of breast cancer patients detailed clinically and observed during 5 years after the surgical treatment. Correlation between TGF-α and/or TNF-α expression and clinical staging - TNM score, lymph node metastasis, tumor recurrence and survival time - was analyzed. According to our present study, the TGF-α positive patients had worse clinical prognosis than the TNF-α positive and double positive cases during long term observation. © 1994 Kluwer Academic Publishers.