The aim of this study was to investigate whether there is a correlation between (99m)Tc-sestamibi uptake and histological malignancy grade in breast carcinoma. Such a correlation could, prior to surgery and histopathological analysis, facilitate selection of patients who need adjuvant therapy. Ninety-six patients with mammographically determined lesions and/or a palpable tumour suspected for malignancy underwent (99m)Tc-sestamibi scintimammography prior to surgery. The final diagnosis was determined by histopathological examination. Benign lesions, cancer in situ and tumours located medially in the breast were excluded. Fifty-three invasive cancer lesions in 53 patients were finally included in the study. Planar scintigraphic breast imaging included two prone lateral projections and one anterior supine projection taken 10 min after injection of 700 MBq (99m)Tc-sestamibi. Focal (99m)Tc-sestamibi uptake in breast lesions was used as the scintigraphic criterion of abnormality. Tumour to background ratios were calculated with partial volume compensation, and histological malignancy grading was performed according to the Elston classification. A correlation was found between (99m)Tc-sestamibi uptake and histological malignancy grade in invasive breast carcinomas ( P<or=0.037).