How would you manage positive surgical margins after partial nephrectomy for kidney cancer?  

If feasible, I would recommend re-excision. This is not always feasible however, and in that case, I would observe. Patients with positive margins do not always recur and thus could spare the patient some toxicity.

Somewhat counter-intuitively, positive surgical margins have not been definitively shown to lead to higher recurrence rates and thus generally no further therapy is advised. Unless there is gross disease left behind we do not generally re-excise. There is no role for other adjuvant systemic therapy ...