A 47-year-old woman patient who presented with weakness in the proximal parts of the upper and lower limbs and difficulty in swallowing was given a diagnosis of advanced esophageal cancer complicated with polymyositis. Steroid therapy was initiated for the polymyositis, but the CK level remained high. Chemotherapy was then selected as the preferred treatment option for the esophageal cancer, however, the treatment was ineffective and the patient died of respiratory failure. There is currently no consensus on the safety of therapy for malignant carcinoma complicated with collagen diseases, therefore, the selection of treatment modality for the disease must be made with care.