Is bilateral lymphadenectomy for midline squamous carcinoma of the vulva always necessary? An analysis from Gynecologic Oncology Group (GOG) 173

Objective To determine which patients with near midline lesions may safely undergo unilateral groin dissection based on clinical exam and lymphoscintigraphy (LSG) results. Methods Patients participating in GOG-173 underwent sentinel lymph node (SLN) localization with blue dye, and radiocolloid with optional LSG before definitive inguinal-femoral lymphadenectomy (LND). This analysis interrogates the reliability of LSG alone relative to primary tumor location in those patients who had an interpretable LSG and at least one SLN identified. Primary tumor location was categorized as lateral (> 2 cm from midline), midline, or lateral ambiguous (LA) if located within 2 cm, but not involving the midline. Results Two-hundred-thirty-four patients met eligibility criteria. Sixty-four had lateral lesions, and underwent unilateral LND. All patients with LA (N = 65) and midline (N = 105) tumors underwent bilateral LND. Bilateral drainage by LSG was identified in 14/64 (22%) patients with lateral tumors, 38/65 (58%) with LA tumors and in 73/105 (70%) with midline tumors. At mapping, no SLNs were found in contralateral groins among those patients with LA and midline tumors who had unilateral-only LSGs. However, in these patients groin metastases were found in 4/32 patients with midline tumors undergoing contralateral dissection; none were found in 27 patients with LA tumors. Conclusion The likelihood of detectable bilateral drainage using preoperative LSG decreases as a function of distance from midline. Patients with LA primaries and unilateral drainage on LSG may safely undergo unilateral SLN.