Navigating lymphatic drainage uncertainty in abdominal ectopic breast cancer: a novel application of indocyanine green fluorescence-a case report and literature review.

Ectopic breast cancer (EBC) is a rare condition in which lymphatic drainage mapping can be challenging due to its variable anatomical locations along the milk line, extending from the axilla to the groin. The EBC arising from the abdominal wall represents a unique challenge, as lymphatic drainage is unpredictable and may involve the axillary and/or inguinal nodal basins. Indocyanine green (ICG) fluorescence has recently emerged as a reliable tracer guiding sentinel lymph node biopsy (SLNB) in orthotopic breast cancer; however, its use in EBC has not yet been reported. Hereby, we report a case of a 64-year-old postmenopausal Caucasian woman who presented with a progressively enlarging mass arising from an ectopic breast tissue in the left upper anterior abdominal wall. Core biopsy revealed invasive papillary carcinoma of breast tissue with associated ductal carcinoma in situ. The patient underwent excision of the ectopic breast tissue involving the EBC with SLNB using ICG fluorescence as the sole tracer. Real-time fluorescence imaging demonstrated lymphatic drainage to the ipsilateral axilla with no inguinal drainage identified. One axillary sentinel lymph node was excised and was negative for metastasis. At one-year follow-up, there was no evidence of recurrence or distant metastasis. To our knowledge, this is the first report describing the use of ICG fluorescence for lymphatic mapping in EBC to guide SLNB. The ability to visualize lymphatic drainage intraoperatively was particularly valuable given the aberrant tumor location and the potential for variable lymphatic drainage pathways. We also reviewed the existing literature on cases of EBC arising from abdominal wall, highlighting the variability in lymphatic drainage patterns and the inconsistent use or underreporting of lymphatic mapping techniques and SLNB, resulting in limited understanding of nodal staging and potential implications for management strategies.