Outcomes of methylene blue single-dye sentinel lymph node biopsy in early breast cancer: a retrospective cohort study from a resource-limited tertiary centre

Abstract Background Sentinel lymph node biopsy (SLNB) is the standard axillary staging procedure for clinically node-negative early breast cancer. Although dual-tracer mapping provides high sentinel-node identification rates, access to radioisotopes and nuclear medicine facilities remains limited in many resource-constrained healthcare systems. We evaluated the technical performance, recurrence outcomes and tracer-related costs of methylene blue (MB)-only SLNB at a tertiary oncology centre in Sri Lanka. Methods This retrospective cohort study included 115 patients with clinically and radiologically node-negative breast cancer who underwent MB-only SLNB. The sentinel-node identification rate was defined as the proportion of attempted procedures in which at least one blue-stained sentinel lymph node was successfully identified. Secondary outcomes included sentinel-node yield, final nodal histology, additional axillary nodal burden, recurrence outcomes and tracer-related costs. Because patients with negative SLNB did not undergo completion axillary lymph node dissection (ALND), a conventional ALND-referenced false-negative rate could not be calculated. Results Sentinel lymph nodes were successfully identified in 113/115 patients, corresponding to an identification rate of 98.3%. Among the 113 successfully mapped patients, sentinel-node tumour deposits were identified in 40 (35.4%), comprising 33 macrometastases, 5 micrometastases and 2 cases with isolated tumour cells, pN0(i+). Seventy-three patients had negative sentinel nodes. The mean sentinel lymph node yield was 3.25 ± 1.70 nodes (mean ± standard deviation). No isolated axillary recurrences were observed among successfully mapped SLNB-negative patients during follow-up (0/73; exact 95% confidence interval 0–4.9%). Overall recurrence occurred in 5/115 patients (4.3%) over a mean follow-up of 36.3 months. No MB-related adverse reactions were recorded. The MB tracer cost was approximately LKR 330 (US$1.10) per patient, and mapping did not require radioisotope procurement, gamma-probe equipment or nuclear medicine support. Conclusions MB-only SLNB achieved a high identification rate, no observed isolated axillary recurrence after negative mapping during short- to mid-term follow-up, and minimal tracer expenditure. These findings support its technical feasibility and practical value where isotope-supported mapping is unavailable. However, the absence of ALND verification in SLNB-negative patients, few recurrence events and no contemporaneous comparator preclude conclusions regarding false-negative rate, diagnostic equivalence, long-term oncologic safety or formal cost-effectiveness. Prospective multicentre comparative studies with longer follow-up are required.