Why would my doctor not recommend radiation therapy after a lumpectomy?

Low risk to recurr: There is a good chance the type of disease was dcis (ductal carcinoma in situ). This is a pre-invasive disease ( not cancer yet). Radiation can be avoided in the most favorable group of patients with dcis since chance of recurrence is very low. Typical conditions met are: 1) large clear margins of resection was obtained, 2) the disease is not too large (size) , 3)not too aggressive ( low-grade).

Ask your doctor why?: This depends on your condition and age. Assuming you have cancer of the breast there are some (by no means all) radiation doctors who may not recommend it if it is early stage and you are over 70 and have good receptors (er and pr) so that you can take a hormone. Best bet is to get a second opinion and likely they won't agree.

It's the right thing: In 1970, no one had lumpectomy (partial mastectomy) and everyone had "radical mastectomy. Today many womaen can avoid mastectomy. The standard is to get roughly 5 weeks of adjuvant radiotherapy to the involved breast. Why because studies proved that no radiotherapy resulted in breast relapse and breast loss. Some women are now choosing to have both breasts removed.

???: You need an opinion from a radiation oncologist so you can adequately understand why you do or don't need treatment. Unless that recommendation was made by someone who specializes in radiation treatments i would hesitate to accept it.

Lumpectomy radiation: Almost all patients who have a lumpectomy need radiation afterwards because of the risk of residual microscopic cancer. A couple of exceptions are in situ cancer that is very small, low grade, and widely clear margins; or invasive cancer that is very small, er +, age over 70, and margins over 2 mm.