Hi Raji ! Good morning. I am Dr Shareef, a general surgeon answering your query. Possibly during and after the chemotherapy you couldn t resume to your normal diet and liquids. Due to this you might have developed constipation and while passing hard stool might have developed a fissure in ano which could be diagnosed only by physical examination of the perianal region. The doctor/surgeon examining you can say with certainty whether it is a fissure or fistula. However, if I were your doctor, after clinically examining you would have advised sitz baths(sitting in a tub of warm water) three times a day, an anti inflammatory, and an antibiotic which covers specially gram negative and anaerobic organisms. I will also add an probiotic and a stool softener to ease you of your pain, and to avoid further trauma to the anal mucosa. This being done, I would also advise you on your diet towards more of roughage and enough liquids to avoid constipation. Most of the acute fissure in ano of recent history usually heal by themselves with this type of conservative management and dietary regulations. However, if the pain increases without much relief, and the fissure is recurring after being cured , then a lateral sphinterotomy surgery with gentle anal dilatation may give you a permanent cure, but you have to continue to keep a watch on your diet. By any chance, if it is a fistula as told by your doctor, the only treatment available is a surgery. This can be decided by the doctor who has examined you, and it is not possible to diagnose it over the net due to obvious reasons. I hope this information helps you in discussion with your doctor for further management. Thanks for choosing healthcaremagic for your health query. Wishing you an early recovery. Dr Shareef.