Breast pains and left underarm pain. could it be cancer?

Could be: While other things also can give you the same problems- such muskuloskeletal related pain, inflammation etc- cancer could be and would be on the differential diagnosis to rule out. Please see your doctor and have a proper breast examination. A mammogram plus minus sonogram may need to be done- as indicated. Good luck.

It's Possible.: While breast cancer can cause pain, most people with breast pain don't have cancer. This is best sorted out by a doctor who can take a thorough medical history, do a careful exam, and possibly order a mammogram and/or ultrasound, depending on your age and the above results. Ideally, they can then alleviate your concerns and actually treat the pain. I suggest you make an appt w/your pcp or gyne.

Heart disease: Depending on your age and risk factors, the symptoms you described are more likely to be due to cardio-vascular disease than breast cancer. Please note that heart disease kills more women than breast cancer. See your doctor asap.