This study is a randomized, comparative trial of postoperative adjuvant therapies in women with HER2 (human epidermal growth factor receptor type-2)-positive primary breast cancer who are ≥70 years of age that will compare trastuzumab (Herceptin®) monotherapy (H group) and trastuzumab in combination with chemotherapy (H+CT group).~The objectives of this study are as follows.~To verify the clinical positioning of trastuzumab monotherapy and combined trastuzumab and chemotherapy as postoperative adjuvant therapies for the treatment of HER2-positive primary breast cancer patients who are ≥70 years of age.~To evaluate the safety of trastuzumab monotherapy and combined trastuzumab and chemotherapy in patients who are ≥70 years of age. In particular, to evaluate cardiac disorders that are a characteristic adverse drug reaction of trastuzumab as well as geriatric-related concerns including lipid metabolism, cerebral infarction and cognitive disorders.~To evaluate overall survival in patients who are ≥70 years of age using trastuzumab monotherapy or combined trastuzumab and chemotherapy.~To evaluate health-related quality of life (HRQOL), cost-effectiveness (utility), and conduct a comprehensive geriatric assessment (CGA) in patients who are ≥70 years of age and using trastuzumab monotherapy or combined trastuzumab and chemotherapy.~To establish and expand information networks by the participation of practitioners in clinical trials that are involved in general clinical practice and breast cancer.
To investigate clinical positioning between trastuzumab (Herceptin) monotherapy (H group) and combination therapy of trastuzumab and chemotherapy (H+CT group) based on a randomized controlled trial in women over 70 years with human epidermal growth factor receptor type-2 (HER2) positive primary breast cancer.