<s>[INST] Hello doctor, My wife is in remission from stage 2 breast cancer. She underwent chemotherapy and radiation last year. As a result of her treatment, she did not have her period for roughly 13 months. Her period returned last month, but she seems to have missed her period this month. My question is, Are irregular periods normal after what she has been through, or is it more common for her cycle to be regular? [/INST] Hello. Loss of ovarian function can happen temporarily or permanently depending on the dosage of the chemotherapy. This happens due to the damage to the immature ovarian follicles containing the immature eggs by the chemotherapeutic agents. So the chances of resumption depend on the ovarian reserve left undamaged. So usually post chemotherapy, a woman may resume her cycles anywhere from a few months to more than a year. Some women may even develop premature ovarian failure. As per your query, irregular cycles are quite common post-chemotherapy once the periods are resumed. But I need to know one more important thing that is the hormone receptor status of the biopsy and whether your wife is on any medication called Tamoxifen. If she is on such medication, then bleeding needs to be monitored by an ultrasound scan to look for the uterine lining thickness. I hope this helps. Ultrasound abdomen and pelvis (in case on any abnormal bleeding pattern). - Keep a track of menstrual cycles. Please connect with me through chat in case you have any further queries on periods. </s>