Could sentinel node mapping of the groin cause extranodal metastasis in vulva cancer?

Groin node lymphadenectomy in vulva cancer carries a substantial risk of morbid sequelae. Sentinel lymph node (SLN) mapping is a valid alternative in patients with squamous cancer of diameter <4 cm and nonsuspicious lymph nodes. SLN are mapped according to the combined technique of radioscintigraphy using technetium-labelled colloid and blue dye. We describe early extranodal recurrence in 2 patients undergoing SLN mapping. They had lymph node metastases at their original dissection. We question whether rapid lymph flow promoted by injection of colloid and dye could cause retrograde flow of cancer cells along the lymphatics draining from the pubis to the groin and extravasation of cancer cells into the dermis since these metastases arose anterior to the pubis and medial to the groin. These recurrence sites were more medial and cephalad than would be expected for skin bridge metastasis. CT imaging shows the metastases are within the dermis. No lymphatic tissue was identified around these subcuticular cancer deposits at repeat resection. Body wall extension occurs in recurrent vulva cancer, but we never saw such an early recurrence when full inguinofemoral lymphadenectomy without SLN was the standard approach. These 2 cases raise a caveat in the application of SLN mapping in vulva cancer, especially when metastasis is detected on SLN as the afferent channels to the lymph nodes may be already blocked or flow impaired by the tumour.