Low Dose Molecular Breast Imaging as a Screening Tool for Women With Dense Breasts

Evaluation of Low-dose Molecular Breast Imaging as a Screening Tool in Women With Mammographically Dense Breasts and Increased Risk of Breast Cancer

A new test for breast cancer screening, molecular breast imaging (MBI) may be more sensitive than mammography for detecting breast cancer in women with dense breasts. The purpose of this study is to see if MBI using a low dose of gamma radiation can find cancers not seen on mammography. Hypotheses: 1. Low-Dose MBI has a significantly higher sensitivity and specificity and equal or higher positive predictive value than SM in women age 40 and older with mammographically dense breasts. 2. Low-dose MBI has comparable sensitivity and specificity to that previously achieved with MBI using a higher dose of radiation. 3. MBI produces a low false positive rate (specificity >90%) that permits its use as a screening tool in this patient population.

A previous study demonstrated that the addition of MBI using 20 mCi Tc-99m sestamibi to screening mammography (SM) increased diagnostic yield for breast cancer in dense breasts (supplemental yield of 7.5/1000 screened). After implementing radiation dose reduction techniques, the performance of incident SM and prevalent screen MBI in women with dense breasts will be compared. Methods: Women presenting for SM with heterogeneously or extremely dense breasts on past prior SM were enrolled and underwent digital SM and MBI. Study information was sent to all eligible patients in advance of their scheduled SM explaining the study and offering them participation. Eligible patients who requested to participate were offered an MBI on the same day as their SM or within 21 days of the SM. Participants may have participated in this screening study up to two times provided at least 24 months had elapsed since the initial MBI scan. This time period was selected as the average time for a tumor to double in size is approximately 20 months. Hence a 24 month time interval between MBI studies was to enable detection of interval cancers or cancers that were too small to be detected in the initial MBI scan. MBI was performed with 8 mCi Tc-99m sestamibi and dual-head cadmium zinc telluride detectors. SMs were read independently; MBIs were read in comparison with SM. MBIs were assigned an assessment score of 1-5 which parallels BI-RADS; scores of 3-5 on MBI were considered positive.

Participants underwent conventional mammography and molecular breast imaging after a 740-millibecquerel (mBQ) (8-mCi) Technetium (99mTc) sestamibi injection.

Molecular breast imaging is a new nuclear medicine technique for imaging the breast. It uses small field of view semiconductor-based gamma cameras that use Cadmium Zinc Telluride detectors. These have superior spatial and energy resolution to conventional sodium iodide detectors.

Mammography is the process of using low-energy X-rays (usually around 30 kVp) to examine the human breast and is used as a diagnostic and a screening tool.

Technetium (99mTc) sestamibi is a pharmaceutical agent used in nuclear medicine imaging. The drug is a coordination complex consisting of the radioisotope technetium-99m bound to six methoxyisobutylisonitrile (MIBI) ligands.

The cancer detection rate per 1000 women screened is the estimate of the number of women with positive results from a screening test.

Recall rate was defined as the percentage of participants recalled for follow-up studies initiated because of abnormal findings with mammography or MBI.

Inclusion Criteria: Past prior SM interpreted as negative or benign [Breast Imaging Reporting and Data System (BI-RADS) Category 1 or 2] Past prior SM interpreted as heterogeneously dense or extremely dense Exclusion Criteria: Subject is unable to understand and sign the consent form Subject is pregnant or lactating Subject is physically unable to sit upright and still for 40 minutes Subject has self-reported signs or symptoms of breast cancer (palpable mass, bloody nipple discharge, axillary mass, etc.) Subject has had needle biopsy within 3 months, or breast surgery within 1 year prior to the study Subject is currently taking tamoxifen, Evista (raloxifene), Zoladex or an aromatase inhibitor for adjuvant therapy or chemoprevention.

Rhodes DJ, Hruska CB, Phillips SW, Whaley DH, O'Connor MK. Dedicated dual-head gamma imaging for breast cancer screening in women with mammographically dense breasts. Radiology. 2011 Jan;258(1):106-18. doi: 10.1148/radiol.10100625. Epub 2010 Nov 2.