Adjuvant therapy based on pathology and molecular subtypes of breast cancer In estrogen receptor-positive patients with poor conventional staging, there is heterogeneity in their molecular staging and sensitivity to chemotherapy and responsiveness to endocrine therapy are not the same. The prognosis of poorer staging due to high T-staging and positive lymph nodes may be influenced by some good molecular biological features, such as hormone receptor positivity, low Ki-67 expression, and low risk for gene 21. When there is inconsistency in staging and staging, single gene and multigene profiling tests may give us more information, but the advantage of multigene testing is currently mainly in the prediction of prognosis, and the prediction of treatment outcome is yet to be further confirmed. Standard chemotherapy should be avoided in patients with poorly staged pathology who have good hormone responsiveness, Her2 negativity, and low proliferation (low risk for 21 or 70 gene expression). It is most important to distinguish between patients who are estrogen receptor positive and those who are negative, as the treatment and prognosis of these two groups of patients are very different. Adjuvant chemotherapy for early-stage breast cancer The goal of adjuvant therapy is to improve the chances of cure by eliminating micrometastatic lesions. About 80% of breast cancer patients are estrogen receptor positive, and for these patients, adjuvant tamoxifen treatment for five years can reduce recurrence rates by 41% and mortality rates by 31%. For pre-menopausal breast cancer patients, tamoxifen remains the standard of care. For post-menopausal breast cancer patients, studies have demonstrated the superiority of aromatase inhibitors over tamoxifen. Data from two large studies, ATAC and BIG1-98, showed that anastrozole and letrozole were more effective than tamoxifen. It is important to monitor bone mineral density in patients treated with aromatase inhibitors; if osteoporosis develops, calcium and vitamin D supplements should be added, along with bisphosphonates and Prolia (denosumab) if necessary. For patients with premenopausal diagnosis of breast cancer, postmenopausal (physiologic or chemotherapeutic effect) use of aromatase inhibitors remains beneficial. Hormonal adjuvant therapy after 5 years Patients with estrogen receptor-positive breast cancer tend to recur after 5 years. For menopausal patients who have been treated with tamoxifen for 5 years, treatment with letrozole, a non-aromatase inhibitor, reduces the relative risk by 42%. For patients who have been treated with tamoxifen for 5 years and are not menopausal, or who cannot tolerate aromatase inhibitors, continued use of tamoxifen may benefit the patient. The results of the international ATLAS (comparing long-term versus short-term adjuvant tamoxifen therapy) study showed that 10 years of tamoxifen reduced late recurrence and mortality in ER+ breast cancer patients compared to 5 years of standard tamoxifen therapy, with better outcomes. The most significant additional benefit of continuing tamoxifen was a reduction in mortality in the second decade after breast cancer diagnosis. The ATTom study yielded the same results. Combining the results of the ATLAS study and the ATTom study, extending adjuvant tamoxifen therapy to 10 years instead of 5 years for estrogen receptor-positive breast cancer may further reduce the risk of recurrence. Compared to no tamoxifen, 10 years of adjuvant treatment with it reduces the risk of death by at least one-third. Chemotherapy Chemotherapy reduces the relative risk of death from breast cancer by one-third, but it does not improve patient survival, as there are many patients who can achieve a cure with surgery and hormone therapy alone. Further research is needed to determine which group of patients needs chemotherapy. We know that the prognosis of patients can be predicted by molecular tests, such as Oncotype DX. In fact, such tests can also identify patients who can be cured with surgery and hormonal therapy. The MINDACT study evaluated the clinical value of adding gene expression profiling to conventional clinicopathological testing to guide adjuvant therapy selection in breast cancer patients. It was designed to spare more patients from adjuvant chemotherapy and achieve a better quality of life. This study is the first attempt to use genetically guided patient classification to reduce the cost of oncology treatment, which not only reflects the concept of giving the right treatment to the right patients, but more importantly, emphasizes that unnecessary treatment should not be given to unsuitable patients. Of course, in the future, we need to identify high-risk patients for better and more adequate treatment and further explore how to incorporate better tumor subgroup classification as well as biological markers predicting efficacy into adjuvant treatment of breast cancer. Even if a breast cancer patient requires chemotherapy, there is a lot to learn about chemotherapy planning. How to develop a chemotherapy plan that reduces patient mortality and chemotherapy-induced side effects is a current issue to consider. HER2-targeted therapy Breast cancer treatment has entered the era of molecular typing. human epidermal growth factor receptor 2 (HER2) positive breast cancer accounts for about 20-30% of all breast cancer patients. HER2 is a clear prognostic indicator for breast cancer. The introduction of trastuzumab, the first humanized monoclonal antibody targeting HER2, has changed the prognosis of HER2-positive breast cancer patients. All clinical studies on adjuvant therapy after breast cancer surgery suggest that surgery plus the anti-HER2 treatment drug trastuzumab improves the DFS rate of patients compared to surgery alone, and most clinical trials have also shown improved OS rates. For patients with large masses that are not suitable for breast-conserving surgery, preoperative adjuvant chemotherapy, HER2-targeted therapy or hormonal therapy can reduce the tumor load and create the conditions for breast-conserving surgery. For those patients with complete pathological remission, especially those with estrogen receptor negative breast cancer, the prognosis is better. Patients with locally advanced breast cancer are best treated with adjuvant chemotherapy before undergoing radical mastectomy. For patients with inflammatory breast cancer with symptoms of erythema and edema, the best treatment is preoperative adjuvant chemotherapy, followed by surgery or radiation therapy as appropriate. Because these patients are unlikely to be hormone receptor positive, it is more likely that they are HER2 gene positive.