Would you consider proceeding with a sentinel lymph node biopsy after wide excision revealed 1.2 mm residual non-ulcerated T2a melanoma on the upper back?  

Any melanoma with Breslow’s depth of more than 0.8 mm (more than T1a) needs a sentinel lymph node biopsy for complete staging, due to higher chance of lymph node metastasis. Ideally, it should be done at the time of wide local excision, as doing the sentinel lymph node biopsy afterwards may be...