Question about radiation treatment

Hello, and thank you for taking the time to review my question.

In April 2008, I was diagnosed with breast cancer, Stage II.  My tumor was 2.6cm.  I've had a mastectomy (right breast).  My CT Scan (of thorax, chest, abdomen, and pelvis) showed *no* abnormalities. No bone scan has been performed to date.

For my sentinel lymph node biopsy a single lymph node was removed: (a) *Intraoperative* diagnosis was Negative.  (b) *Post-operative* immunohistochemical staining diagnosis revealed a "single cluster of keratin positive cells. This cluster measures 0.10 mm."

Additional (axiliary) lymph nodes were *not* removed.  And, I'm currently undergoing chemotherapy (ACx4, Tx4) treatment.

Given the above data for my diagnosis, my question is this:  after I finish chemo treatment, should I highly consider getting radiation treatment (in the underarm -- lymph node -- area)?  My concern is the 0.10 mm (small?) keratin cluster that was found in the sentinel lymph node.  Also, *no* axiliary lymph nodes were removed.

Thank you.  

-Krista

[Cleveland Clinic]

Dear Krista:  Radiation therapy is generally reserved for women who have known large numbers of affected lymph nodes as the purpose of radiation therapy is local control of disease.  A single inmmunohistochemically positive lymph node suggests that there is low likelihood of gross metatstatic disease in other lymph nodes and, by itself, would not usually be an indication for radiation therapy.  Of course, there are additional factors about an individual cancer which may increase or decrease risk and may make an oncologist consider additional therapy based on the risk benefit ratio.  You should discuss your situation with your oncologist and, if you are concerned, consider an appointment with a radiation oncologist who can discuss the possible benefits and risks as they pertain to your situation.