Xpert Breast Cancer STRAT4 Assay using fine-needle aspiration biopsy samples in a resource-constrained setting: a prospective diagnostic accuracy study.

Use of fine-needle aspiration biopsy (FNAB) specimens on Xpert Breast Cancer STRAT4 Assay, a CE-marked in-vitro diagnostic medical device, could potentially increase access to breast cancer biomarker testing in resource-constrained settings. We aimed to assess the performance of a research use-only version of STRAT4 using FNAB specimens in Tanzania.

Patients aged 18 years or older with palpable breast masses presenting to the FNAB Clinic at Muhimbili National Hospital in Dar es Salaam, Tanzania were recruited consecutively. Patients who were pregnant, lactating, or had a previous diagnosis of breast cancer were excluded. STRAT4 testing was performed on off-label FNAB samples using four protocols: the 1x protocol on FNAB smears (1x FNAB), quick lysis and Maui protocols (both on FNAB smears), and the 1x protocol on formalin-fixed paraffin-embedded cell block material (1x cell block). The primary outcomes were overall concordance, sensitivity, specificity, and area under the receiver operating characteristic curve of STRAT4 as compared with immunohistochemistry or immunohistochemistry plus fluorescence in-situ hybridization.

Between Nov 29, 2017, and Dec 17, 2020, 208 patients were enrolled. Of 208 cases, 51 (25%) were excluded from analysis because of insufficient tissue in the cell block or absent cell blocks, leaving 157 participants (all female) for analysis. For estrogen receptor, 1 × FNAB had the best performance, with an overall concordance of 95% (95% CI 90–100). For HER2, Maui had the highest agreement, with an overall concordance of 93% (95% CI 89–98.

Processing FNAB samples with STRAT4 is feasible in Tanzania, and performance for the estrogen receptor is robust. Further optimization of STRAT4 for FNAB has the potential to improve timely access to breast cancer diagnostics in resource-constrained settings.