Objectives: The purpose of this study was to determine the sensitivity of breastspecific gamma imaging (BSGI) in the detection of invasive breast cancers and to characterise the sensitivity of BSGI based on tumour size and pathological grade. Methods: 139 females with invasive carcinoma who underwent BSGI were retrospectively reviewed. Patients were injected in the antecubital vein with 20-30 mCi (925-1110 MBq) of 99m Tc-sestamibi. Images were obtained with a high-resolution, breast-specific gamma camera (Dilon 6800; Dilon Technologies, Newport News, VA) and were categorised based on radiotracer uptake as normal, normal with heterogeneous uptake, probably abnormal and abnormal. For a positive examination, the region of the area of increased uptake had to correlate with the laterality and location of the biopsy-proven cancer. Results: 149 invasive cancers in 139 patients with a mean size of 1.8 cm (0.2-8.5 cm) were included. 146 were identified with BSGI (98.0%). All cancers which measured $0.7 cm (n5123) as well as all cancers grade 2 or higher (n5102), regardless of tumour size, were identified with BSGI (100%). There were 6 cancers that were pathological grade 1 and measured ,7 mm, of which 50% (3/6) were identified with BSGI. The overall sensitivity of BSGI for the detection of invasive breast cancer is 98.0%. The sensitivity for subcentimetre cancers is 88.5% (23/26). Conclusion: BSGI has a high sensitivity for the detection of invasive breast cancer. Our results demonstrate that BSGI detected all invasive breast cancers pathological grade 2 and higher regardless of size and all cancers which measured $7 mm regardless of grade. BSGI can reliably detect invasive breast cancers and is a useful adjunct imaging modality for the diagnosis of breast cancer. Mammography has remained the modality of choice for breast cancer screening. Nevertheless, it is an imperfect examination with a sensitivity of 78-85% that declines to 68% in females with dense breasts [1][2][3][4][5][6]. The limitations of mammography have resulted in the development of adjunct imaging modalities to improve breast cancer detection. Most frequently, ultrasound is used in conjunction with mammography as an adjunct imaging modality for breast cancer diagnosis, particularly in females with dense breasts [2].Mammography and ultrasound are both anatomical approaches for the diagnosis of breast cancer. Nuclear medicine techniques that utilise physiological properties of tumours are increasingly being used. A meta-analysis of scintimammographic studies using a traditional, general purpose gamma camera demonstrated an average sensitivity of 84% for breast cancer detection, although many of the cancers included in these studies were palpable and larger [7]. However, scintimammography with a general purpose gamma camera is limited in the detection of non-palpable cancers and cancers less than 1 cm in size because of intrinsic resolution limitations [8][9][10][11]. Another limitation is the inability of a general purpose gamma camera to image in positions...