When is postmastectomy radiation therapy indicated for a de-novo occurrence of cancer in the chest wall after mastectomy without prior malignancy, such as in a patient who had prophylactic mastectomy?  

This is such a rare occurrence and I may have done this a few times. I have usually limited to CW only if SNLN is done as part of surgery and is negative. That being said, feel local excision alone with adjuvant systemic treatment as indicated may be an option.