Introduction: Occult primary breast cancer, i.e., isolated axillary adenocarcinoma without detectable tumor in the breast by either physical exam or mammography, represents up to 1% of operable breast cancer. Modified radical mastectomy (MRM) is generally the accepted treatment for this condition although tumor is identified in only two-thirds of mastectomy specimens. Breast magnetic resonance imaging (MRI) can identify occult breast carcinoma and may direct therapy. This study examined the ability of breast MRI to detect occult breast cancer and to facilitate breast conservation therapy.
Methods: Forty women with biopsy-proven metastatic adenocarcinoma to an axillary lymph node and no evidence of primary cancer were studied. All patients had a physical examination, mammography, and MRI of the breast. Using a dedicated breast coil, MRI imaging was performed with and without gadolinium enhancement. Positive MRI scans were compared with histopathologic findings at the time of operation (n = 21).
Results: MRI identified the primary breast lesion in 28 of 40 women (70%). Of these 28 patients, 11 had MRM, 11 had lumpectomy/axillary lymph node dissection (ALND)/radiotherapy (XRT), 2 had ALND/XRT alone, and 4 had no local treatment secondary to stage IV disease. Two women initially treated with lumpectomy/ALND subsequently had mastectomy for positive margins. Of the women with positive MRI who had breast surgery, 21 of 22 (95%) had tumor within the surgical specimen. Twelve women had negative MRI of the breast. Five of these 12 underwent MRM, of whom 4 had no tumor in the mastectomy specimen. The remaining 7 patients had ALND and whole breast radiation (ALND/XRT) (n = 5), or were observed (n = 2). Overall, 18 of 34 women surgically treated had MRM, while 16 (47%) preserved their breast. Tumor yield for patients having breast surgery was 81%.
Conclusions: MRI of the breast can identify occult breast cancer in many patients and may facilitate breast conservation in select women. Negative breast MRI predicts low tumor yield at mastectomy.