Combination chemotherapy with pertuzumab, trastuzumab, and docetaxel is recommended as the first-line treatment for patients with HER2-positive unresectable or metastatic breast cancer. We report 2 cases of unresectable breast cancer for which pertuzumab, trastuzumab, and docetaxel therapy was effective. Case 1: A woman in her 40s was diagnosed with TxN3aM0, Stage ⅢC, HER2-positive, hormone receptor-positive advanced breast cancer. After administration of 6 courses of pertuzumab, trastuzumab, and docetaxel therapy, she underwent surgery(Bt+Ax[Ⅱ]). Histopathological examination revealed that chemotherapy effect was Grade 3. Case 2: A woman in her 60s was diagnosed with de novo Stage Ⅳ, HER2- positive, hormone receptor-negative breast cancer. She was administered 8 courses of pertuzumab, trastuzumab, and docetaxel therapy as the third-line treatment, because she initially refused treatment. Thereafter, she underwent surgery(Bt+Ax [Ⅰ]). In both cases, histopathological examination revealed complete response after chemotherapy. Thus, combination therapy of pertuzumab and trastuzumab may improve the prognosis in patients with HER2-positive breast cancer.