There may be a promising new treatment on the horizon for advanced breast cancer patients, according to developing research.

Researchers are studying the cancer-killing drug trastuzumab rezetecan for those with ERBB2-low metastatic breast cancer, whose tumors have low levels of HER2, a protein that can help cancer cells grow.

A phase 3 clinical trial called HORIZON-Breast06 sought to determine whether the drug works better than standard chemotherapy for patients with this cancer type.

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The researchers analyzed 551 female patients across 73 hospitals in China who were randomly assigned to receive either the drug intravenously every three weeks, or the physician’s choice of chemotherapy. The study period lasted from June 2023 to August 2025.

The drug significantly delayed cancer progression compared with chemotherapy, giving patients more than a year before their cancer began growing again.

The median time without tumor growth was 16.4 months compared to 6.8 months with chemo.

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Patients who received trastuzumab rezetecan were 73% less likely to have their cancer worsen or die during the study than patients who received chemotherapy.

The drug appeared to delay cancer progression in patients with both hormone receptor-positive and hormone receptor-negative breast cancer.

The results were published in JAMA.

Tumors shrank in 75.5% of patients who received the drug, compared with 41.2% of those who received chemotherapy.

At the 12-month mark, 90.6% of trastuzumab rezetecan patients were alive, compared to 81.4% of chemo patients.

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The authors concluded that trastuzumab rezetecan provided "significant progression-free survival benefit over physician’s choice of chemotherapy in patients with ERBB2-low advanced breast cancer."

Loren Rourke, a Texas-based breast surgical oncologist and author in Texas, called the results "incredibly encouraging."

"When you're talking about women living with advanced breast cancer, those months matter," Rourke, who was not involved in the study, told Fox News Digital. "They represent more time when the cancer is being held in check and potentially more opportunities to enjoy life without the disease getting worse."

What makes these findings especially exciting, according to the oncologist, is that the treatment showed benefits across different types of breast cancer.

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"It's another important step forward, and it gives us genuine reason to be hopeful," she said. "A treatment that can keep cancer from progressing for a longer period has the potential to make an enormous difference in a patient's life."

While the drug may cause fewer serious lung problems than similar treatments, it was linked to other side effects, including anemia and other blood-related problems.

Serious side effects occurred in more than 84% of patients who received the new drug, compared with nearly 68% of those who received chemotherapy.

Rourke emphasized the importance of considering the side effects, "because more time without cancer progression doesn't automatically mean better quality of life."

"We need to better understand the side effects, particularly the significant decreases in blood counts that can lead to fatigue, anemia and increased risk of infection," she said.

The researchers acknowledged that toxicity occurred more frequently and often required dose modification, although they said these effects were "generally manageable."

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The experts agreed that more research is needed.

"As exciting as these findings are, there are still important questions we need to answer," Rourke told Fox News Digital. "We know this treatment delayed cancer progression, but we don't yet know whether it will help patients live longer. That's an important distinction."

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"It's important to celebrate meaningful progress while making sure we're asking the right questions about what comes next."

• A new study explored the differences between tumors in younger and older colon cancer patients.
• Younger patients sometimes had more aggressive, treatment-resistant forms of colon cancer.
• Staying active, cutting down on processed foods, and getting screened are good ways to lower risk.

People under 50 aren't only at a higher risk of colon cancer today than they were a few decades ago. They're also developing a different, sometimes more aggressive form of it compared to older patients, scientists say.

A new study published in Nature Medicine analyzed 189 tumors from colorectal cancer patients aged 29 to over 90, including measurements of gene activity in more than 850,000 cancer cells.

The goal was to look at how tumors varied "across the entire spectrum of age," Dr. Ana Anderson, a co-senior author of the study who leads the cancer immunology program at the Gene Lay Institute at Brigham and Women's Hospital in Boston, told Business Insider. "Is it the same colon cancer but just happening in younger people, or is there something different about it?"

As a result, the study was able to map out gradual, subtle differences in colorectal cancer tumors correlated with age. While the researchers couldn't pinpoint exactly why tumors in younger people look different, Anderson said the study is an exciting starting point for further research.

"There's a lot of interest in lifestyle factors and environmental exposures as potential contributors; however, nothing specific has been pinned down," Anderson said. "What we did is take a rather simple but comprehensive approach just to try to understand the disease itself."

Younger patients' tumors had a different cellular makeup

The study's researchers couldn't definitely state that colon cancer in younger patients is always more aggressive — that would require more study.

However, what they did find was that younger patients "generally have more aggressive disease and they are generally more resistant to the standard of care therapies, which is mostly chemotherapy," Anderson said.

Tumors in younger patients generally had a higher presence of supporting and connecting cells known as stromal cells. Stromal cells, such as fibroblasts, can produce factors that suppress the immune response, making it harder for chemotherapy drugs to work. "They essentially can form a shield that protects the tumor from infiltration," Anderson said.

The study found that the presence of stromal cells generally declined from younger to older patients, and the youngest patients tended to have the highest number of stromal cells in proportion to cancer cells.

The reverse was true for the oldest patients, who generally had the fewest stromal cells and the highest numbers of cancer cells.

Researchers narrowed down where to look for answers

Younger patients also had higher activity of long non-coding RNAs (lncRNAs), which are associated with cellular signaling in cancer. The study also found gene activity in younger patients that suggested stronger signaling between cells — potentially helping cancer cells move and invade nearby tissue.

The problem is, lncRNAs are still a fairly recent discovery; they only became linked to cancer research in the late 2000s, with some poorly understood ones referred to as "dark RNAs." "A lot of them have just not been researched, and that's why they're called 'dark RNAs' — it's a big mystery," Anderson said.

For that reason, she said it was the finding she considered most promising. "There's a world of biology to be discovered there — we know where to focus our research efforts," she said.

Anderson, an immunologist, also hopes to explore the presence of immune cells in younger colon cancer cases, as immune cells are involved in killing cancer cells but were "under-captured" in this study, she said. "There are many types of immune cells," she said. "Are there different subsets that are more present in the young tumors or absent in the young tumors versus the older tumors?"

Reduce your risk with these simple habits

While the study doesn't present any immediate new takeaways for young people concerned about colon cancer, Anderson suggested following existing guidance for lowering your risk.

She noted that the recommended screening age for most people was lowered from 50 to 45 a few years ago, but that it's wise to see a doctor sooner if you experience common colon cancer symptoms like rectal bleeding, abdominal pain, bloating, or changes in bowel movements.

If you're "extra cautious," she said, it's never a bad idea to stay active and cut down on inflammatory foods such as ultraprocessed snacks and alcohol.