One To Watch

Tesaro

Company Overview

A GSK-owned oncology-focused biotech headquartered in Waltham, Massachusetts, best known for developing the PARP inhibitor niraparib (Zejula) and advancing a broad immuno-oncology pipeline spanning ovarian, prostate, and bladder cancers. Originally an independent Nasdaq-listed company, Tesaro was acquired by GlaxoSmithKline in a $5.1 billion deal that closed in early 2019, cementing GSK's push into the oncology space. The unit continues to operate as a center of oncology drug development and commercialization within GSK, with niraparib and dostarlimab (Jemperli) serving as its cornerstone commercial and clinical assets.

Headquarters and Global Presence

Tesaro is headquartered in Waltham, Massachusetts, with a European subsidiary, Tesaro Europe Limited, supporting commercial and regulatory operations across EU markets. As part of GSK, the unit benefits from a global infrastructure spanning the US, Europe, and Asia.

Founding and History

Tesaro was founded in 2010 by Mary Lynne Hedley and Manuel Llorente with a mission to develop and commercialize oncology medicines. Its first approved product, Varubi (rolapitant), an NK-1 receptor antagonist for chemotherapy-induced nausea, received FDA approval in October 2015. Niraparib (Zejula) followed, receiving FDA approval in 2017 after priority review and a June 2017 action date. GSK completed the $5.1 billion acquisition of Tesaro in 2019, transforming it from a standalone biotech into the cornerstone of GSK's oncology division.

Therapy Areas and Focus

Tesaro focuses exclusively on oncology, with primary programs in gynecologic cancers — particularly ovarian, fallopian tube, and primary peritoneal cancer — as well as prostate and bladder cancer. The unmet need in BRCA-mutated and homologous recombination-deficient tumors underpinned the niraparib strategy, while the immuno-oncology pipeline targets broader patient populations via checkpoint inhibition. Tesaro's CMO has emphasized that efficacy beyond BRCA mutation status is central to Zejula's long-term differentiation and market potential.

Technology Platforms and Modalities

Tesaro's core platform centers on PARP inhibition, exploiting synthetic lethality in DNA damage repair-deficient tumors to selectively kill cancer cells. Niraparib is a potent, selective PARP-1 and PARP-2 inhibitor designed for once-daily oral dosing, offering a practical advantage in maintenance therapy settings. The company has layered an immuno-oncology strategy on top, developing antibodies targeting checkpoint pathways including PD-1 (TSR-033, an anti-LAG-3 antibody) and pursuing combinations of PARP inhibition with checkpoint blockade. Most recently, Tesaro secured rights to Alteogen's ALT-B4 enzyme to develop a subcutaneous formulation of dostarlimab, extending the platform into drug delivery innovation.

Key Pipeline and Programs

Niraparib (Zejula) is Tesaro's lead commercial asset — a small-molecule PARP inhibitor approved in the US and Europe for maintenance treatment of adult patients with recurrent epithelial ovarian, fallopian tube, or primary peritoneal cancer. It has received EU marketing authorization as monotherapy and is reimbursed in the UK via the Cancer Drugs Fund. Janssen (J&J) holds exclusive worldwide rights to niraparib in prostate cancer under a global licensing deal, while Takeda has rights for the Japanese market worth up to $340 million, and Zai Lab holds rights for China.

Dostarlimab (Jemperli) is a PD-1 blocking antibody developed under the Tesaro/GSK umbrella, with Tesaro securing exclusive global rights in January 2026 to Alteogen's ALT-B4 enzyme to enable a subcutaneous formulation. This next-generation delivery approach aims to improve patient convenience and broaden dostarlimab's commercial reach.

TSR-033 is an investigational anti-LAG-3 antibody being evaluated in Phase I/II trials as a monotherapy and in combination with anti-PD-1 therapy across multiple solid tumor types. The NCT03250832 study includes a dose-escalation phase (Part 1a) and a combination expansion phase to establish the recommended Phase II dose across selected tumor indications.

Recent Developments

In January 2026, Tesaro secured an exclusive license from South Korean biotech Alteogen for global rights to the ALT-B4 enzyme, enabling development of a subcutaneous formulation of dostarlimab — a strategically significant move to differentiate Jemperli against competing PD-1 inhibitors. In November 2025, a legal dispute erupted between Tesaro/GSK and AnaptysBio, with both parties filing lawsuits alleging breach of a cancer drug partnership deal; AnaptysBio shares fell 14% in pre-market trading on the news. A US court subsequently dismissed AnaptysBio's anticipatory breach claim in April 2026, giving Tesaro a procedural win in that litigation. Earlier, in June 2024, Tesaro prevailed in the latest stage of its patent dispute with AstraZeneca over Zejula.

Key Personnel

Mary Lynne Hedley, one of Tesaro's co-founders, serves as President and Chief Operating Officer, bringing deep expertise in oncology drug development from the company's inception. Martin Huber serves as Chief Medical Officer, having spoken publicly about Zejula's differentiation beyond BRCA mutation status and its competitive positioning against Lynparza in the PARP inhibitor market. William Aitchison serves as Senior Vice President of Technical Operations, overseeing manufacturing and supply chain functions for the commercial and clinical portfolio.

Strategic Partnerships

Tesaro has constructed a global partnership network around niraparib: Janssen Biotech holds exclusive worldwide rights to niraparib in prostate cancer under a licensing deal, Takeda holds Japanese rights worth up to $340 million, and Zai Lab holds rights for China with potential for two immuno-oncology programs. In manufacturing, WuXi AppTec's STA Pharmaceutical signed a five-year supply agreement with Tesaro for niraparib production. Tesaro has also collaborated with Roche to evaluate niraparib alongside Tecentriq (atezolizumab) in metastatic bladder cancer, and with Merck using Myriad Genetics' myChoice HRD platform to identify responders to niraparib plus Keytruda (pembrolizumab) combinations.

FAQ Section

Tesaro serves as the operational center of GSK's oncology unit following the $5.1 billion acquisition completed in 2019. It provides GSK with two commercialized assets — niraparib and dostarlimab — and a clinical-stage immuno-oncology pipeline that GSK had previously lacked. The acquisition was viewed by analysts as a high-cost entry into oncology with uncertain near-term returns, but dostarlimab's growing approvals and the push into subcutaneous formulation underscore GSK's commitment to building the franchise.

PARP inhibitors exploit synthetic lethality — when a tumor cell already carries a defect in homologous recombination repair (as seen in BRCA1/2-mutated cancers), blocking PARP-mediated base excision repair creates a second hit that causes cell death. Niraparib selectively inhibits PARP-1 and PARP-2, and its efficacy has been demonstrated in both BRCA-mutated and non-BRCA homologous recombination-deficient tumors, broadening its eligible patient population beyond earlier PARP inhibitors. This breadth of activity is central to Tesaro's argument that Zejula can compete effectively against AstraZeneca's Lynparza.

Tesaro's CMO has emphasized efficacy beyond BRCA mutation status as the key differentiator — niraparib demonstrates clinical benefit in patients who would not qualify for BRCA-restricted PARP inhibitor approvals. Niraparib is also dosed once daily orally without a companion diagnostic requirement for all approved indications, offering practical advantages in the maintenance setting. Tesaro has secured a global licensing network — including Janssen for prostate cancer and Takeda for Japan — that extends the drug's reach into indications and geographies where AstraZeneca's Lynparza may not hold exclusivity.

Dostarlimab is an approved PD-1 blocking antibody commercialized by GSK/Tesaro for endometrial cancer and other mismatch repair-deficient solid tumors. In January 2026, Tesaro signed an exclusive global license with Alteogen for the ALT-B4 hyaluronidase enzyme, which enables subcutaneous co-formulation of biologics and would allow dostarlimab to be administered via injection rather than intravenous infusion. This subcutaneous program is in development and represents a meaningful convenience upgrade and potential differentiator in the increasingly crowded PD-1 inhibitor market.

Tesaro operates almost exclusively in oncology, with gynecologic malignancies — particularly ovarian, fallopian tube, and primary peritoneal cancer — as the historical anchor. The pipeline has expanded into prostate cancer via the Janssen partnership on niraparib, bladder cancer through a collaboration with Roche combining niraparib and Tecentriq, and broader solid tumors through the TSR-033 anti-LAG-3 program. The combination of PARP inhibition and checkpoint immunotherapy reflects a strategy to extend benefit beyond DNA repair-deficient cancers into immunologically active tumor types.

TSR-033, the anti-LAG-3 antibody, is in Phase I/II development, with a dose-escalation study (NCT03250832) establishing the recommended Phase II dose as monotherapy and in combination with anti-PD-1 therapy across selected solid tumor types. Dostarlimab is already commercially approved, making it the most advanced immuno-oncology asset. The subcutaneous dostarlimab program enabled by ALT-B4 is in early development. Key milestones include Phase II data readouts for TSR-033 combinations and regulatory submissions for the subcutaneous dostarlimab formulation.

The key catalysts and risks for Tesaro include:

Litigation outcome: The AnaptysBio lawsuit remains an active legal risk despite the April 2026 dismissal of the anticipatory breach claim; a final resolution could affect partnership strategy and financial exposure.
Subcutaneous dostarlimab: Clinical and regulatory progress on the ALT-B4-enabled formulation is a near-term catalyst that could meaningfully boost Jemperli's commercial profile.
PARP inhibitor competition: Continued competitive pressure from AstraZeneca's Lynparza and other PARP inhibitors in overlapping indications remains an ongoing headwind for Zejula's market share.
TSR-033 Phase II data: Combination data with anti-PD-1 therapy in solid tumors will be critical in determining whether TSR-033 progresses into registrational trials or is deprioritized.

Want to Update your Company's Profile?