6. Unexplained Weight Gain or Loss
"If you suddenly put on 5 pounds, I wouldn't worry," Runowicz says. But gaining excess weight month to month -- especially if you usually maintain a normal weight and watch what you eat -- can be due to a buildup of fluid in the belly related to ovarian cancer and warrants a checkup with your doctor, she says.
Unexplained weight loss of 10 pounds or more "may be the first sign of cancer," the American Cancer Society says, and is most often linked to pancreatic, stomach, esophagus, or lung cancer.
But weight loss in women is often caused by a hyperactive thyroid, Runowicz says. Expect your doctor to order a thyroid test first to check for this common disease.