On May 6, Cumoxicillin Capsules (Saitanxin®), the world's first CDK2/4/6 inhibitor independently developed by Chia Tai Tianqing Pharmaceutical Group Co., Ltd., a subsidiary of China Biopharmaceutical (01177.HK), received approval from the National Medical Products Administration (NMPA) for its combination with fulvestrant for the initial treatment of patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative locally advanced or metastatic breast cancer. This is the second indication approved for the marketing of Cumoxicillin Capsules, providing a new treatment option for first-line treatment of HR-positive advanced breast cancer patients in China.

Last December, cumoxicillin was approved in combination with fulvestrant for the treatment of HR+/HER2- breast cancer patients whose disease has progressed after prior endocrine therapy, and it is estimated that it has already benefited thousands of breast cancer patients in clinical practice. This new approval is primarily based on the CULMINATE-2 clinical trial, which showed that cumoxicillin in combination with fulvestrant significantly prolonged progression-free survival compared to placebo in combination with fulvestrant, and demonstrated good long-term safety.

Breast cancer is the leading cause of cancer death among women worldwide and in China. According to the International Agency for Research on Cancer, nearly one million new cases of breast cancer are diagnosed globally each year, and nearly 400,000 new cases are diagnosed in China annually. HR+/HER2- breast cancer is the most common subtype, accounting for approximately 65%-70% of all breast cancers. Guidelines such as the Chinese Society of Clinical Oncology (CSCO) Breast Cancer Guidelines (2026 Edition) and the Chinese Anti-Cancer Association Breast Cancer Diagnosis and Treatment Guidelines (2026 Edition) both recommend CDK4/6 inhibitors combined with endocrine therapy as a first-line treatment for HR+/HER2- advanced breast cancer. However, the resulting CDK4/6 inhibitor resistance and myelosuppression have become pressing clinical challenges.

Cumoxicillin, the world's first CDK2/4/6 inhibitor, offers a more comprehensive mechanism for inhibiting cell cycle signaling pathways, providing a new approach to overcoming drug resistance. Building upon traditional CDK4/6 inhibitors, cumoxicillin exhibits potent inhibition of CDK2, and this triple blockade of CDK signaling pathways helps delay the development of CDK4/6 inhibitor resistance in clinical practice. Furthermore, while maintaining highly effective CDK4 inhibition, cumoxicillin selectively reduces its effect on CDK6, which, compared to traditional CDK4/6 inhibitors, helps reduce the risk of severe myelosuppression. Based on this mechanistic innovation, cumoxicillin offers a novel and superior efficacy option for first-line treatment to delay drug resistance or for second-line treatment to overcome drug resistance.

The approval of this new indication is primarily based on the results of the CULMINATE-2 clinical trial. The CULMINATE-2 study demonstrated that cumoxicillin in combination with fulvestrant as first-line treatment for HR+/HER2- advanced breast cancer achieved an objective response rate of 59.3%, reduced the risk of disease progression or death by 44%, and had a grade ≥3 neutropenia incidence of only 20.3% and a treatment discontinuation rate due to adverse events of only 3.5%. It also showed stable benefits in patients with visceral metastases and premenopausal women, providing a new option for overcoming CDK4/6 inhibitor resistance. Furthermore, the long-term safety of this treatment is controllable and easily managed.

Cumoxicillin has significant clinical potential, with its development plan covering the entire treatment cycle for HR-positive breast cancer. Specifically, its combination with fulvestrant for HR+/HER2- advanced breast cancer that has progressed after prior endocrine therapy was approved for marketing in China on December 9, 2025. The much-anticipated adjuvant therapy for HR+ early breast cancer is also underway, with enrollment completed and follow-up currently in progress.

Currently, breast cancer is a global hot topic for innovative drugs.A fiercely contested market. According to Frost & Sullivan, the global breast cancer market is projected to reach $69.9 billion by 2030, with the Chinese market reaching $17.2 billion (a 10-year CAGR of 8%), making it one of the largest and most certain-growth sub-sectors in the global oncology field. China's biopharmaceutical industry has consistently focused on innovation based on clinical treatment needs, gradually building a highly competitive product pipeline in the global breast cancer field.

According to relevant sources, focusing on the field of breast cancer treatment, China Biopharmaceutical 's product line not only comprehensively covers the molecular subtypes of HER2+, HER2 low expression, HR+/HER2-, and triple-negative breast cancer (TNBC), but also systematically covers the entire treatment cycle from neoadjuvant therapy and adjuvant therapy to first- and second-line and above treatment for advanced breast cancer, striving to provide more breast cancer patients with new treatment options.

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