Tc-99(m)-MIBI scintimammography in 300 consecutive patients: Factors that may affect accuracy

We evaluated the diagnostic yield of Tc-99(m)-MIBI scintimammography in a r elatively large series of consecutive patients referred for breast surgery on the basis of physical examination or mammogram. Tc-99(m)-MIBI uptake was correlated to tumour size, receptor status, neovascularity, proliferating activity, P-170 glycoprotein expression and the patient's gonadal state. Th ree hundred consecutive patients referred to our institution, with either a positive mammogram or a palpable mass, were entered into the study. All pa tients underwent Tc-99(m)-MIBI scintimammography. Pathological status was o btained after surgery in all patients. Breast cancer was diagnosed in 218 ( 73%) patients. The MIBI scan was positive in 89% (194/218) cancer patients and in 17% (14/82) of patients with benign masses (false-positives); the sc an was negative in 24 (11%) cancer patients (false-negatives). The sensitiv ity of MIBI scintigraphy was higher for tumours >1 cm (95 vs 48% in lesions less than or equal to 1 cm) and in pre-menopausal women (95 vs 85%). Conve rsely, the specificity was better for lesions <1 cm (100%) and in post-meno pausal women (89%). The positive predictive value of MIBI scan was good bot h in small (<1 cm) and large tumours (100% and 93%, respectively) and sligh tly modified by gonadal state (89% and 96% in pre- and post-menopausal stat e). The negative predictive value was unsatisfactory, especially in small t umours and in older patients. The diagnostic performance increased stratify ing data for tumour size, indicating that lesion size is a major determinan t in the diagnostic accuracy of MIBI scintimammography. We conclude that 99 Tcm-MIBI scintimammography is useful in the diagnostic evaluation of young patients, because it can select patients for further invasive diagnostic pr ocedures. In older patients, a positive 99Tcm-MIBI scan is highly suggestiv e of malignancy and might be an indication for surgery. In the case of a ne gative scan, biopsy is advisable given the poor negative predictive value. Small tumour size and a well-differentiated histotype characterize false-ne gative cases. (C) 1999 Lippincott Williams & Wilkins).