Thanks for your question on Health Care Magic. I can understand your concern. No, this is not common. Foul smelling discharge in rectal cancer patient suggest infection at tumour site. Chemotherapy makes patient immunocompromised. So chances of infection are high in these patients. Radiotherapy weakens local defense system. So both these make patient prone to infection. So better to get done culture and sensitivity report of discharge. Culture report will isolate the causative organism and sensitivity report will guide you better about effective antibiotic treatment. He needs antibiotics. Hope I have solved your query. Wishing good health to your father. Thanks.