Lynparza (olaparib), a product of Fortune 500 pharmaceutical firm Merck and Fortune 500 Europe company AstraZeneca, exhibited clinically meaningful improvements in overall survival, among other promising findings, in people with germline BRCA-mutated (gBRCAm), HER2-negative high-risk early breast cancer. About 87.5% of patients treated with the drug were alive after six years, compared to 83.2% who received a placebo. Long-term results of the OlympiA phase 3 trial were presented Dec. 11 at the San Antonio Breast Cancer Symposium.

“The durable long-term efficacy seen in the OlympiA study reinforces Lynparza as an important treatment option for those living with this truly challenging, very aggressive form of breast cancer,” Dr. Eliav Barr, senior vice president, head of global clinical development, and chief medical officer of Merck Research Laboratories, said in a news release about the findings.

HER2-negative refers to cancer cells whose surfaces lack a protein called human epidermal growth factor receptor 2. Such cells tend to grow more slowly than HER2-positive ones, according to the National Cancer Institute (NCI), and are less likely to recur or spread throughout the body. Breast, bladder, stomach, ovarian, and pancreatic cancers all may be HER2-negative. BRCA1 and BRCA2 are breast cancer genes, and an inherited error in one of them is called a germline mutation. About 13% of women will develop breast cancer, compared to more than 60% of women with an inherited BRCA mutation, the NCI says.

“These data reinforce the importance of germline BRCA testing at the time of diagnosis, so we can identify all eligible patients who may benefit from treatment with olaparib as early as possible,” Dr. Judy Garber, co-principal investigator of the trial and chief of the division of cancer genetics and prevention at the Dana-Farber Cancer Institute in Boston, said in the news release.

Dr. Douglas Marks, an oncologist at NYU Langone Health and medical director of the clinical trials office at Perlmutter Cancer Center – Long Island, attended the symposium at which the research was presented and says the results were well-received.

“This has been a big advance in the field,” Marks tells Fortune. “This was a follow-up analysis [but] it’s more added reassurance.”

The OlympiA trial began in 2014 and is slated to run through mid-2029. The Food and Drug Administration approved Lynparza in 2022 based on primary trial results published in the New England Journal of Medicine in 2021. The drug, according to Merck, is the first and only PARP inhibitor—a type of medication that “causes a disruption in the way that [patients’] cells work,” Marks explains—to improve overall survival in early breast cancer.

At the median six-year follow-up, trial patients who took Lynparza had a 28% reduced risk of death versus the placebo. The drug also showed clinically meaningful improvements in invasive disease-free survival (IDFS) and distant disease-free survival (DDFS).

“Invasive disease-free survival means getting another—not precancer, not another noninvasive—but another invasive breast cancer, either in the breast or chest wall or distant,” Marks explains. “Distant disease-free survival is having the cancer actually come back as an advanced breast cancer.”

Lynparza patients had a 79.6% IDFS rate at six years, compared to 70.3% for placebo patients, with the drug reducing the risk of invasive breast cancer recurrence, second cancers, or death by 35%. DDFS rates were 83.5% and 75.7% for Lynparza and placebo patients, respectively. Patients given the drug had a 35% reduced risk of distant disease recurrence or death.

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Early detection critical to long-term breast cancer survival

The ongoing OlympiA trial involves more than 1,800 adults diagnosed with gBRCAm, HER2-negative high-risk early breast cancer, early being the operative word. That means the cancer hasn’t spread beyond the breast and regional lymph nodes and is amenable to surgery, says Dr. Halle Moore, director of breast medical oncology at the Cleveland Clinic Taussig Cancer Institute.

Lynparza is an oral prescription medication designed to be taken daily, and trial participants in the treatment group took the tablets for a year. It’s administered after a patient has completed surgery and chemotherapy. While the drug is also FDA-approved for patients with metastatic breast cancer, meaning the disease has spread to other parts of the body, the trial focused only on early diagnoses.

Having been an oncologist for a quarter-century, Moore has seen clinical trial data fluctuate. It’s not uncommon for promising primary results to become less significant over time, she says. That wasn’t the case for this Merck-AstraZeneca study.

“What we saw here was that the benefits in terms of reducing the risk of recurrence of breast cancer and improving survival persisted and actually numerically got larger over time, did not diminish,” Moore tells Fortune. “The last analysis they had done was at about four years follow-up on average and at this presentation, they had just over six years…the benefits seem to be increasing over time.”

About 5% to 10% of female breast cancer patients have a BRCA mutation, according to the American Cancer Society. When breast cancer is diagnosed early, the five-year relative survival rate is over 99%, but plummets to 32% for distant-stage disease.

For more on breast cancer:

• A 5-minute test can estimate your odds of developing breast cancer—but not if you’re biracial
• Women will now be notified about breast density after mammograms. Here’s what should happen next
• The doctor who caught actress Olivia Munn’s breast cancer also diagnosed her own: ‘I don’t want another woman to go through what I went through’
• Many women find their own breast cancer. So why are breast self-exams no longer recommended?
• Mammograms should start at 40 to address rising breast cancer rates at younger ages, panel says