There are many reasons breast cancer can metastasize (spread). Whether it's because a patient fails to have regular screenings or a doctor fails to diagnose the breast cancer, the disease can reach the most advanced stages of development without being detected.

Generally, diagnosing the spread of the disease requires a doctor to discover it through any of the various diagnostic tests, such as bone scans, computed tomography (CT) scans or magnetic resonance imaging (MRI) tests.

Breast cancer can be classified as having metastasized even if it hasn’t reached any distant organs. If this is the case, and only the lymph nodes have been affected, the prognosis is likely to be much better. If the breast cancer has spread to distant organs, the fewer organs that are affected, the better the prognosis should be. For example, if the breast cancer has only spread to the lungs, the prognosis typically would be much better than if it has spread to the lungs, liver and the bones.

There is also encouragement to be found in the make-up of the cancer itself. If the cancerous cells contain estrogen and progesterone hormone receptors, the cancer may respond much better to certain treatment options. Anti-estrogen therapies typically have much more success in patients with breast cancer that has estrogen and progesterone hormone receptors.

After prolonged exposure to therapy and treatment, sometimes tumors begin to become resistant. As a result, if the tumor remains highly responsive to hormonal therapy and chemotherapy, the prognosis for the patient will generally be higher. Because of this, those patients who haven’t undergone several rounds of treatment and therapy previously should be more responsive to treatment for metastatic breast cancer. If the metastatic breast cancer has resulted from a recurrence of a previous cancer, treatment for it will generally be more effective if a good deal of time has passed since the previous cancer treatments.

There are several symptoms to be wary of if you’ve been diagnosed with breast cancer. These symptoms may indicate that the cancer has begun spreading to other areas of the body and can include bone pain, shortness of breath, lack of appetite, unexplained weight loss or headaches. These symptoms can be triggered by any number of bodily conditions, however. If you have advanced breast cancer and you experience any of the above symptoms, your doctor may wish to perform further diagnostic tests to check for metastasis.