Abstract Breast cancer is the leading malignancy in women and the second most frequent cancer globally. Earlier identification of breast cancer can improve treatment outcomes and prevent metastasis beyond the breast. Traditional screening tests are not sensitive enough for early diagnosis and have extended detection periods. Recent studies have explored several Breast cancer biosensor techniques, including optical, electrical, electrochemical, and mechanical biosensors. This paper proposes a circle with a large plus sign refractive index biosensor for the identification of two distinct breast cancer cells namely, MDA-MB-231 and MCF-7. The highest sensitivity has been observed 1714.28 nm/RIU for the MDA-MB-231 and 1714.28 nm/RIU for the MCF-7. The highest quality factor (QF) value for NC1(normal cell of MDA-MB-231) is 10.52, for CC1(cancer cell of MDA-MB-231) is 11.94, for NC2 (normal cell of MCF-7) is 10.64, and for CC2 (cancer cell of MCF-7) is 12.09. The value of detection limits (DL) for NC1 is 0.1573, for CC1 is 0.1360, for NC2 is 0.1554, and for CC2 is 0.1341. This proposed sensor can highly sense the breast cancer biomarkers.