BACKGROUND: HER2-positive breast cancer occurs in about 15-20 % of all breast cancers. It is both a prognostic and predictive biomarker and the introduction of anti-HER2 therapy over the last 20 years has significantly improved outcomes in this subset of patients, so that they are now comparable to or better than those of patients with HER2-negative tumors. Approximately 5-10% of patients are diagnosed with metastatic breast cancer. It was good news for these patients when, on April 17, 2020, the FDA approved tucatinib in combination with trastuzumab and capecitabine for adult patients with advanced unresectable or metastatic HER2-positive breast cancer who had received one or more prior anti-HER2-based regimens in the metastatic setting. The efficacy of the regimen was demonstrated in the HER2CLIMB trial, which enrolled 612 patients with HER2-positive metastatic breast cancer who had previously been treated with trastuzumab, pertuzumab, and/or trastuzumab emtansine. Median overall survival for patients in the tucatinib arm was 21.9 months (95% CI 18.3-31.0) compared with 17.4 months (95% CI 13.6-19.9) for patients in the control arm (HR 0.66; 95% CI 0.50-0.87; P = 0.00480). CASE: Our patient is a middle-aged woman without visceral metastatic involvement, but with extensive nodal involvement, skeletal metastatic involvement and left breast almost completely consumed by tumor. This woman had a more or less successful three lines of anti-HER2 therapy and the fourth line of one-year-long systemic treatment with the cytostatic eribulin. The inclusion of tucatinib with trastuzumab and capecitabine in the fifth line of systemic therapy achieved a very nice partial regression of the primary tumor without significant toxicity. CONCLUSION: In this case report, we describe the case of a highly pretreated patient with HER-2 positive metastatic breast cancer.

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