Sep 11, - Menopause also causes you to gain more body fat and lose lean muscle. It's common for women who have chemotherapy to gain about 5 to 14 pounds over a year. Women treated with steroids may also put on pounds, but the weight gain is usually seen only after weeks of continuous use.What Might Cause Me to · Do Other Breast Cancer. Weight gain after diagnosis is common among women with breast cancer, yet results . We categorized weight change as >5% loss; maintained within (plus or.