Why radiation after a mastectomy? i have already had chemo pre surgery

Local reccurence: The goal is to reduce risk for local reccurence. Will depend of certain factors include - the size of the cancer, the number of lymph nodes involved and the location of the lymph nodes, positive margin. If the cancer is large- more than 5 cm, if there are more than 3 lymph nodes involved with cancer on arm pit, if margin is positive etc- post mastectomy would be recommended. Discuss w/oncology team.

Local recurrences: After mastectomy there is some breast tissue left along back of skin & chest wall. Ctx is most effective at lowering chance of tumor recurring distantly from breast and lymph nodes by killing microscopic cells n the blood if they r there. Radiation after mrm further reduces the chance of tumor recurring n chest wall or nodes. >4ln's, tumor>5cm, or + margin are indications. Increases survival.