Risovalisib (Haizexin, 海泽欣), a selective PI3Kα inhibitor, has been approved by Japan’s Ministry of Health, Labour and Welfare (MHLW) for the treatment of PIK3CA-mutated ovarian clear cell carcinoma (OCCC) in patients whose disease has progressed after chemotherapy. Supported by data from the phase II CYH33-G201 study, this approval introduces a targeted therapeutic option for a historically treatment-resistant subtype of ovarian cancer. Importantly, the approval is accompanied by the authorization of the AmoyDx® PIK3CA Mutation Detection Kit, a companion diagnostic designed to identify eligible patients based on tumor PIK3CA mutation status, reinforcing a precision oncology approach to treatment selection.
Background
Ovarian clear cell carcinoma (OCCC) represents a distinct and aggressive subtype of epithelial ovarian cancer, characterized by unique molecular features and limited responsiveness to conventional chemotherapy. Patients with advanced or recurrent disease often face poor outcomes, highlighting a significant unmet clinical need for more effective, targeted treatment strategies.
One of the most relevant molecular alterations in OCCC is mutation of the PIK3CA gene, which drives activation of the PI3K/AKT/mTOR signaling pathway and promotes tumor growth, survival, and resistance to therapy. This has positioned the PI3K pathway as a critical therapeutic target in this disease.
Regulatory Approval In Japan
Japan’s Ministry of Health, Labour and Welfare (MHLW) has approved risovalisib mesylate (Haizexin, 海泽欣) for the treatment of PIK3CA-mutated ovarian clear cell carcinoma in patients whose disease has progressed after chemotherapy. The approval was granted on March 23, 2026, based on data from the pivotal phase II CYH33-G201 study.
Risovalisib is an oral, once-daily therapy administered at a dose of 40 mg under fasting conditions, offering a convenient targeted treatment option in the post-chemotherapy setting.
This approval marks an important milestone for Haihe Biopharma, representing one of the company’s innovative oncology therapies to reach the Japanese market and addressing a clear gap in treatment for this molecularly defined population.
Companion Diagnostic And Precision Medicine Approach
A key component of this approval is the parallel authorization of the AmoyDx® PIK3CA Mutation Detection Kit, developed as a companion diagnostic to support patient selection.
This real-time PCR-based assay is designed to detect PIK3CA gene mutations in tumor tissue samples, enabling clinicians to identify patients who are most likely to benefit from PI3Kα-targeted therapy. The test uses DNA extracted from formalin-fixed, paraffin-embedded (FFPE) tumor tissue and plays a central role in implementing precision oncology in clinical practice.
The integration of a companion diagnostic ensures that treatment is aligned with tumor biology, improving therapeutic efficiency while minimizing unnecessary exposure in patients unlikely to respond.
Risovalisi: Mechanism Of Action
Risovalisib is a selective inhibitor of the PI3Kα isoform, targeting tumors driven by PIK3CA mutations, a common oncogenic event in ovarian clear cell carcinoma.
The PI3K pathway plays a central role in regulating cellular processes such as proliferation, metabolism, and survival. In normal physiology, PI3K activation is tightly controlled; however, in tumors harboring PIK3CA mutations, this pathway becomes constitutively active, leading to continuous downstream signaling through AKT and mTOR, ultimately promoting tumor growth and resistance to apoptosis.
By selectively inhibiting PI3Kα, risovalisib:
- Suppresses downstream AKT signaling
- Inhibits mTOR pathway activation
- Reduces tumor cell proliferation
- Promotes apoptosis in cancer cells
This targeted mechanism allows for a more precise therapeutic approach compared with conventional chemotherapy, which lacks molecular specificity.
Clinical Evidence
The approval of risovalisib is primarily based on findings from the phase II CYH33-G201 trial, which evaluated its efficacy and safety in patients with PIK3CA-mutated ovarian clear cell carcinoma who had progressed after prior chemotherapy.
The study demonstrated meaningful anti-tumor activity, supporting the clinical benefit of targeting the PI3K pathway in this population. While adverse events were observed, the safety profile was consistent with the mechanism of action of PI3K inhibitors, with commonly reported toxicities including:
- Hyperglycemia
- Rash
These effects are considered on-target toxicities, reflecting the role of the PI3K pathway in metabolic regulation and skin homeostasis.
Clinical Significance
The approval of risovalisib represents a shift toward biomarker-driven treatment in ovarian clear cell carcinoma. Historically, OCCC has been associated with:
- Limited sensitivity to platinum-based chemotherapy
- Distinct molecular characteristics compared with other ovarian cancer subtypes
- Poor prognosis in advanced or recurrent settings
By directly targeting a key oncogenic driver, risovalisib introduces a precision oncology strategy that aligns treatment with tumor genetics, potentially improving outcomes in a patient population with few effective options.
The simultaneous approval of a companion diagnostic further strengthens this approach, ensuring accurate patient selection and maximizing therapeutic benefit.
Key Takeaway
The approval of risovalisib (Haizexin) in Japan establishes a new targeted treatment option for patients with PIK3CA-mutated ovarian clear cell carcinoma, combining molecularly guided therapy with companion diagnostic testing to advance precision oncology in a challenging disease setting.