Journal club: molecular breast imaging at reduced radiation dose for supplemental screening in mammographically dense breasts

Abstract

OBJECTIVE. The purpose of this study was to assess the diagnostic performance of supplemental screening molecular breast imaging (MBI) in women with mammographically dense breasts after system modifications to permit radiation dose reduction. SUBJECTS AND METHODS. A total of 1651 asymptomatic women with mammographically dense breasts on prior mammography underwent screening mammography and adjunct MBI performed with 300-MBq (99m)Tc-sestamibi and a direct-conversion (cadmium zinc telluride) gamma camera, both interpreted independently. The cancer detection rate, sensitivity, specificity, and positive predictive value of biopsies performed (PPV3) were determined. RESULTS. In 1585 participants with a complete reference standard, 21 were diagnosed with cancer: two detected by mammography only, 14 by MBI only, three by both modalities, and two by neither. Of 14 participants with cancers detected only by MBI, 11 had invasive disease (median size, 0.9 cm; range, 0.5-4.1 cm). Nine of 11 (82%) were node negative, and two had bilateral cancers. With the addition of MBI to mammography, the overall cancer detection rate (per 1000 screened) increased from 3.2 to 12.0 (p < 0.001) (supplemental yield 8.8). The invasive cancer detection rate increased from 1.9 to 8.8 (p < 0.001) (supplemental yield 6.9), a relative increase of 363%, while the change in DCIS detection was not statistically significant (from 1.3 to 3.2, p =0.250). For mammography alone, sensitivity was 24%; specificity, 89%; and PPV3, 25%. For the combination, sensitivity was 91% (p < 0.001); specificity, 83% (p < 0.001); and PPV3, 28% (p = 0.70). The recall rate increased from 11.0% with mammography alone to 17.6% (p < 0.001) for the combination; the biopsy rate increased from 1.3% for mammography alone to 4.2% (p < 0.001). CONCLUSION. When added to screening mammography, MBI performed using a radiopharmaceutical activity acceptable for screening (effective dose 2.4 mSv) yielded a supplemental cancer detection rate of 8.8 per 1000 women with mammographically dense breasts.

Keywords: 99mTc-sestamibi; breast cancer; mammographic density; molecular breast imaging; supplemental screening.

Figures

Fig. 1

Flowchart shows study protocol. MBI = molecular breast imaging, DCIS = ductal carcinoma in situ.

Fig. 2

Mammographically occult invasive lobular carcinoma in 54-year-old woman detected by molecular breast imaging (MBI). A, Right craniocaudal image from digital screening mammography was interpreted as negative. B, Adjunct craniocaudal MBI image was interpreted as multifocal area of marked radiotracer uptake in upper outer right breast. Final pathology was multifocal node-negative grade I invasive lobular carcinoma more than 4 cm in extent on MBI, with largest individual mass being 0.6 cm.

Fig. 3

Multifocal mammographically occult invasive ductal carcinoma detected by molecular breast imaging (MBI) in 78-year-old woman. A, Left mediolateral oblique image from digital screening mammography was interpreted as negative. B, Adjunct left mediolateral oblique image from MBI was interpreted as focal area of marked radiotracer uptake in lower inner left breast (arrow). Final pathology was multifocal node-negative grade I invasive ductal carcinoma, with largest mass (2 cm) visualized by MBI.

Fig. 4

Small mammographically occult invasive ductal carcinoma detected by molecular breast imaging (MBI) in 70-year-old woman. A, Left mediolateral oblique image from digital screening mammography was interpreted as negative. B, Adjunct left mediolateral oblique image from MBI was interpreted as focal area of mild radiotracer uptake in upper outer left breast (arrow). Final pathology was node-negative 0.5-cm grade I invasive ductal carcinoma.

Fig. 5

Small molecular breast imaging (MBI)-occult invasive ductal carcinoma detected by mammography in 49-year-old woman. A, Left craniocaudal image from digital screening mammography was interpreted as showing focal asymmetry in lower inner left breast (arrow) that was less conspicuous on diagnostic evaluation and was recommended for short-interval follow-up in 6 months, at which time biopsy was performed. B, Adjunct craniocaudal image from MBI obtained at time of screening mammography was interpreted as negative. Final pathology was 0.3-cm grade II invasive ductal carcinoma.