Abstract P2-08-18: De-Escalating Axillary Surgery in Nigeria: a phase II Single Arm Trial Protocol

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Abstract Introduction: Breast cancer is the most common cancer and cause of cancer related mortality in Nigeria. The majority of women present with locally advanced disease. The current standard of care for these women is neoadjuvant chemotherapy (NAC) followed by modified radical mastectomy, including complete axillary lymph node dissection (ALND). Within the last decade, the de-escalation of axillary surgery has been extended to women who present with clinically node positive (cN1) disease who are converted to clinically node negative (cN0) after NAC. In this setting, a sentinel lymph node biopsy (SLNB) is performed using a dual-tracer localization technique with methylene blue and Tc-99 sulfur colloid. This is prohibitive to axillary de-escalation in many low- and middle-income countries (LMICs) where the nuclear medicine infrastructure, to support access to Tc-99 sulfur colloid lymphoscintigraphy, is limited. To overcome the challenge posed by the dearth of Tc-99 radiocolloid in Nigeria, this study seeks to evaluate the feasibility and efficacy of pre-operative axillary ultrasound (aUS) and a single agent (methylene blue) SLNB to stage the axilla in women converted from cN1 to cN0 disease after NAC. Methods: This is a phase II, single arm trial being conducted at Obafemi Awolowo University Teaching Hospital (OAUTH) Ile-Ife, Nigeria. Initial inclusion criteria include: women ≥ 18-70 years of age, biopsy confirmed invasive carcinoma of the breast and clinically palpable N1 disease (cN1). Eligible patients have an aUS and if abnormal nodes are present the most suspicious undergoes core biopsy and clip placement. Patients with pathology confirmed TanyN1M0 disease will undergo NAC with curative intent as per institutional standards at the discretion of the treating surgeon. Patients with a clinical complete response (cN0) at the completion of NAC will have a pre-op aUS. At the time of the operation, 5ml of 1% methylene blue is injected in an intra-parenchymal fashion with a 5-minute message. A sentinel lymph node will be classified as blue and/or suspicious by the operating surgeon. Surgeons performing the procedure have obtained additional training in the SLNB technique. Each sentinel lymph node will be removed and labelled separately and sequentially. A completion ALND (level 1-2) will be performed as per institutional practice and the contents labelled separately. Performance of the pre-operative clinical exam, aUS, SLNB and clipped node will be determined for each eligible patient. The study as research ethics board approval from OAUTH and was registered on clinicaltrials.gov prior to study initiation (NCT06039956). Results: As of June 2024, 37 patients have met initial inclusion criteria and have been consented and enrolled into the study. Nine of these have completed NAC and 6 have gone on to receive surgery as per the study protocol with a methylene blue only SLNB followed by completion axillary dissection. We expected to enrol 50 patients within the first year of the study. Target enrolment is 210 patients, which assumes a pCR of 30% and a FNR of 20% with 80% power to report on performance characteristics of the study intervention with 95% confidence intervals. Discussion: Tc-99 sulfur colloid is not readily available in many LMICs. We have designed and commenced the implementation of a protocol to study the de-escalation of axillary surgery for women who present with locally advanced, node positive breast cancer in a low-resource environment using readily available technology. Citation Format: Gregory Knapp, Olalekan Olasehinde, Rheann Brownstone, Omisore Oluwatosin, Adewale Aderounmu, Funmilola Wuraola, Toyosi Teniola Sotala, Omolade Betiku, Anya Romanoff, Folasade Adeyemi, Victoria Mango, Marcia Edelweiss, T. Peter Kingham, Olusegun Alatise. De-Escalating Axillary Surgery in Nigeria: a phase II Single Arm Trial Protocol [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P2-08-18.

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