This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oncology, Subject name: Surgery
A 45-year-old woman presents with a pigmented lesion on her right thigh. She undergoes an incisional biopsy which reveals malignant melanoma with a thickness of 3 mm. Findings on examination of the groin are normal. Which of the following is the most appropriate next step in management? 
Select and explain. 
A. Wide local excision with a 1-cm margin, followed by radiotherapy, B. Wide local excision with a 1-cm margin and groin lymph node dissection, C. Wide local excision with a 2-cm margin and sentinel lymph node biopsy, D. Wide local excision with a 2-cm margin and groin lymph node dissection
C: Wide local excision with a 2-cm margin and sentinel lymph node biopsy
Answer: C: Wide local excision with a 2-cm margin and sentinel lymph node biopsy 
Explanation: Melanoma with a thickness of 3 mm is managed with a wide local excision with a 2-cm margin. Wide local excision for malignant melanoma with thickness: < 1 mm - 1 cm margin, 1-4 mm - 2 cm margin, > 4 mm - 2 to 3 cm margin This should be followed by sentinel lymph node biopsy. It is the first node that drains a paicular nodal basin. It is identified by: intra-operative injection of blue dye. preoperative injection of 99m Tc sulphur colloid around the lesion and detection with a gamma counter intraoperatively. If this comes positive, it is followed by a complete lymph node (LN) dissection. Malignant Melanoma is a radio-resistant tumor.