After a mastectomy, what factors determine if radiation therapy is recommended for a breast cancer patient?
Traditionally the indications for post-mastectomy radiation have been as following:
- A tumor 5cm (2 inches) or larger
- 4 or more lymph nodes involved by cancer
- Inflammatory Breast Cancer
- when the surgical margins of the mastectomy specimen are grossly or closely involved with cancer
About a decade ago, studies from Denmark and Canada revealed benefit of post-mastectomy radiation for women with 1-3 involved lymph nodes. Even though initially in the US we were slow to accepting these data, independent studies in US have convinced most of radiation oncologists in the US to recommend post-mastectomy radiation not only to post-menopausal but also premenopausal women with less than 4 lymph nodes involved.
Even though the above-mentioned factors continue to be indications for radiation after mastectomy a few challenges have been introduced to these seemingly straightforward indications in the past decade. This is mainly due to sentinel lymph node biopsy replacing most of complete axillary lymph node dissections, introductions of PET imaging and also increase in use of neoadjuvant chemotherapy.
The challenge sentinel lymph node biopsy has introduced is that often the number of lymph nodes removed are less than 4. The question of whether additional nodes need to be removed if one or more of these sentinel lymph nodes are involved, has been subject of debate amongst surgical, radiation and medical oncology experts for years. The recent publication of the results of the American College of Surgeons Oncology Group trial (Z0011) put this issue to rest because it showed that completion axillary dissection in these patients did not add local control or survival benefit. But it also left radiation oncologists in a dilemma regarding the necessity for irradiating the lymph nodes for patients with positive SLNs who do not undergo ALND is uncertain. So this issue is often addressed by assessing the individual’s risk of having residual disease in the axilla.
When chemotherapy is administered prior to mastectomy, it can potentially completely destroy the cancer cells. That is an ideal outcome but would not eliminate the need for mastectomy. In such a scenario, the challenge for the radiation oncologist is whether postmastectomy radiation is necessary or not. If a sentinel node biopsy is performed prior to the administration of chemotherapy, the status of the lymph nodes prior to chemotherapy may provide helpful information regarding this dilemma, otherwise the radiation oncologist does not have such a basis for making the recommendation. The jury is still out on this issue and individualized recommendations must be based on taking other factors predictive of risk of local recurrence.
PET scans might suggest involvement of internal mammary nodes. Because of the risk of false-positivity and the fact that these nodes are not normally sampled or dissected, the decision regarding treating these potential positive lymph nodes by irradiating them becomes another subject of discussion at tumor boards.
So as you can appreciate, practice of radiation oncology, like many other fields in medicine is moving away from one size fits all towards individualized medicine.