In what situations would you treat elective regional lymph nodes for a squamous cell carcinoma of the skin on the extremity/trunk that was clinically node negative?

Nodal metastasis from small, to medium size [up to 3 cm in diameter] squamous cell carcinoma on the extremity is not that common. Considering the morbidity of nodal treatment in a patient with clear margins of resection I would not prophylactically treat the nodes. If the tumor shows perineural or l...