Stage IIA breast collision tumor: disease-free after surgery and adjuvant therapy

What happened, in summary

This 72-year-old woman came to the hospital after noticing a lump in the right breast. She had a history of ovarian serous carcinoma, hypertension, and gallbladder polyps, and her sister had also had breast cancer. Imaging showed what initially looked like one irregular mass in the upper-inner right breast, but ultrasound and contrast-enhanced CT suggested 2 adjacent tumors with different internal features. There were no visible systemic metastases and no axillary lymph-node enlargement. Core needle biopsy showed invasive ductal carcinoma of no special type with heterogeneous immunohistochemistry. One component was luminal B, with ER 95%, PR 5%, HER2 IHC 1+, and Ki-67 20%. The second component was luminal B/HER2-positive, with ER 95%, PR 15%, HER2 IHC 3+, and Ki-67 20%. The clinical stage was cT2N0M0 / Stage IIA. A hereditary breast and ovarian cancer syndrome was considered because of her personal and family history, but BRCA genetic testing was not performed because of age and cost constraints. She underwent total mastectomy with sentinel lymph-node biopsy. Pathology confirmed invasive ductal carcinoma made up of 2 distinct tumor subtypes separated by fibrous stroma, consistent with a collision tumor. The final pathologic stage was pT2N0M0 / Stage IIA. This mixed biomarker pattern mattered because the HER2-positive component supported HER2-targeted treatment while the hormone receptor-positive profile supported endocrine therapy. After surgery, she received 4 cycles of epirubicin plus cyclophosphamide, followed by 4 cycles of docetaxel with trastuzumab. Trastuzumab was then continued every 3 weeks as monotherapy, and she later began endocrine therapy with an aromatase inhibitor. At the most recent follow-up, 4 years after surgery, she remained disease-free.