Current and Emerging Therapies for HER2-Positive Women With Metastatic Breast Cancer

Abstract

CASE STUDY DE, a 31-year-old premenopausal woman with a nonsignificant medical history, noticed a right breast mass after playing basketball in September 2011. She initially attributed the mass to slight trauma, but after 2 weeks, she realized the mass was increasing in size. Her primary care physician ordered a bilateral screening mammogram and ultrasound. Mammography revealed no evidence of malignancy in the left breast. In the right breast, at the 7 o'clock position, a loose cluster of faint calcifications spanned a 2.2-cm area. Ultrasound confirmed an irregular hypoechoic mass in the right breast measuring 3.5 × 2.7 × 2.8 cm. Ultrasound of the right axilla identified two enlarged right axillary lymph nodes. Ultrasound core-needle biopsy of the suspicious right breast mass confirmed invasive ductal carcinoma, nuclear grade 2, Ki67 index of 55%, estrogen receptor-positive (H score of 180), progesterone receptor-positive (H score of 135), HER2-positive (3+ on immunohistochemistry). Utilizing the TNM (tumor, node, metastasis) staging system, she was clinically staged with a stage IIB (cT2, cN1, M0) invasive breast tumor. The computerized axial tomography (CT) scan of the chest, abdomen, and pelvis demonstrated the known right breast mass and two enlarged right axillary lymph nodes; however, no metastatic disease was noted. Nuclear bone scan revealed no bone metastases. Her medical oncologist recommended she receive neoadjuvant chemotherapy. The patient was treated with 6 cycles of neoadjuvant docetaxel at 75 mg/m², carboplatin at an AUC (area under the curve) of 6, and trastuzumab (Herceptin) at 6 mg/kg (TCH), which she tolerated well. She then underwent a right segmental mastectomy with axillary lymph node dissection and was found to have a residual 1.0-cm invasive ductal carcinoma, representing a 60% tumor volume reduction. None of 13 axillary lymph nodes were positive for disease. Pathologic staging confirmed a stage IA (ypT1, ypN0, M0) tumor. DE completed 33 fractions of radiation therapy to the right breast. She initiated endocrine therapy with tamoxifen at 20 mg daily and received 1 year of maintenance trastuzumab (6 mg/kg). Due to vaginal discharge and weight gain, endocrine therapy was switched from tamoxifen to toremifene (Fareston), which she tolerated relatively well. She continued routine follow-up, with no evidence of disease. In September 2014, DE presented to her primary care physician complaining of left hip pain. Magnetic resonance imaging (MRI) of the left hip revealed T2 hyperintense masses within the right anterior superior iliac crest, right sacrum, and left iliac body consistent with skeletal metastases. She was referred back to her medical oncologist, and per National Comprehensive Cancer Network (NCCN) guidelines, a biopsy of the suspicious lesion was obtained. The bone biopsy of the lytic lesion was consistent with metastatic breast cancer, which was estrogen receptor-positive, progesterone receptor-positive, and HER2-positive (3+ on immunohistochemistry). Restaging CT scan of the chest, abdomen, and pelvis revealed new 4- to 6-mm pulmonary nodules, hilar and mediastinal lymphadenopathy, new liver lesions, and bone lesions. Nuclear bone scan confirmed multiple bone metastases of the right and left iliac bones and sternum. Complete blood cell count with differential and complete metabolic panel were within normal ranges. The CA 27-29 tumor marker for breast cancer was elevated at 495 U/mL (normal range, < 37 U/mL). DE was understandably devastated by the new diagnosis. She questioned how the treatment plan was to be established. Her medical oncologist struck a somewhat optimistic tone. He explained that metastatic breast cancer was not yet considered to be curable, but periods of disease stability and chronicity were possible. He explained that the HER2 positivity was perhaps the most important factor in delineating her treatment options. He told her that current treatment options were numerous and increasing in number.