Breast cancer occurs when cells in the breast divide and grow without normal control. Between 50 and 75 percent of breast cancers begin in the ducts, 10 to 15 percent begin in the lobules and a few begin in other breast tissues .
Tumors in the breast tend to grow slowly. By the time a lump is large enough to feel, it may have been growing for as long as 10 years. However, some tumors are aggressive and grow much more rapidly.
It is important to understand the difference between invasive breast cancer and non-invasive breast cancer, called ductal carcinoma in situ (kar-sin-O-ma in SY-too, sometimes called DCIS).
Invasive breast cancer:
Invasive breast cancer occurs when abnormal cells from inside the ducts or lobules break out into nearby breast tissue. This allows the cancer cells to spread to the lymph nodes and, in advanced stages, to organs like the liver, lungs and bones (a process called metastasis). Cancer cells can travel from the breast to other parts of the body through the blood stream or the lymphatic system. They may travel early in the process when the tumor is small or later when the tumor is large.
Non-invasive breast cancer - ductal carcinoma in situ (DCIS):
When abnormal cells grow inside the milk ducts, but have not spread to nearby tissue or beyond, the condition is called ductal carcinoma in situ (DCIS). The term "in situ" means "in place". With DCIS, the abnormal cells are still "in place" inside the ducts. DCIS is a non-invasive breast cancer (you may also hear the term “pre-invasive breast carcinoma”).
Although the abnormal cells have not spread to tissues outside the ducts, they can develop into invasive breast cancer.
Male breast cancer:
Male breast cancer is cancer that forms in the breast tissue of men. Though breast cancer is most commonly thought of as a woman's disease, male breast cancer does occur.
Male breast cancer is most common in older men, though male breast cancer can occur at any age.
Men diagnosed with male breast cancer at an early stage have a good chance for a cure. Still, many men delay seeing their doctors if they notice unusual signs or symptoms, such as a breast lump. For this reason, many male breast cancers are diagnosed when the disease is more advanced.