Muscular changes in carcinomas of the breast

14 samples of the Musculus pectoralis major from patients with early stages of breast cancer and 3 samples from patients with nonmalignant mammary diseases were stored in liquid nitrogen and investigated histologically, histochemically and histometrically. Main changes are lipomatosis, fibre necrosis, occasionally perifascicular atrophy, metabolic changes (e.g. accumulation of lipids), and alterations of the activity of oxidative enzymes. Histometrically we found an atrophy of type 2-fibres. There may be relations between the degree of the muscle changes and the severity of the tumour disease. The paraneoplastic muscle disease is a "concomitant myopathy" and may be regarded as a "functional myopathy". In its development we can differentiate a phase of compensation and a phase of decompensation.