Some of these responses are what we would call exceptional
At Dana-Farber Cancer Institute, researchers have taken a meaningful step against one of oncology's most disproportionately lethal cancers — a rare subtype that accounts for nearly half of endometrial cancer deaths while representing only a small fraction of cases. By pairing a guided molecular weapon with an immune system liberator, they achieved measurable tumor reduction in more than a third of patients who had already exhausted most of their options. The result is not a cure, but it is a signal — one that points toward a future where treatment might be matched more precisely to the biology of each patient's disease.
- Serous endometrial cancer kills with a ferocity wildly disproportionate to its rarity, and patients who reach the third or fourth line of treatment have almost nowhere left to turn.
- A Dana-Farber trial tested whether combining a tumor-targeting antibody-drug conjugate with an immune checkpoint inhibitor could break through where prior therapies had failed — and in 6 of 16 heavily pre-treated patients, it did.
- One patient's cancer disappeared entirely; two others remained progression-free for nearly a year or more, results that oncologists in this field describe as exceptional.
- The combination appears to work by having the antibody-drug conjugate reshape the tumor's immune environment, allowing the checkpoint inhibitor to do what it normally cannot in this cancer subtype.
- Researchers are now moving toward molecular analysis to identify who will respond and who will resist, with the aim of extending benefit and personalizing future trials.
At Dana-Farber Cancer Institute, researchers have found a promising foothold in one of gynecological oncology's most stubborn problems. Serous endometrial cancer is rare — just 5 percent of all endometrial cases — yet it accounts for roughly 40 percent of deaths from the disease. The 16 patients enrolled in this trial had already been through one to four rounds of prior therapy. Their options were running out.
Into that difficult terrain, the team introduced a pairing of mirvetuximab soravtansine, an antibody-drug conjugate that delivers a potent anti-cancer payload directly to cells bearing a specific surface marker, and pembrolizumab, an immune checkpoint inhibitor that releases the immune system's brakes. Six patients saw their tumors shrink — one completely, five partially. The trial met its primary endpoint. Two patients remained progression-free for extended periods, one for nearly a year, another for more than 18 months.
The logic behind the combination is precise. The antibody-drug conjugate targets folate receptor-alpha, which appears at high levels in this cancer subtype. Checkpoint inhibitors alone tend to fail in these tumors, but preclinical evidence suggested the conjugate might alter the immune microenvironment in ways that allow the inhibitor to finally take hold — increasing T cell infiltration and amplifying the immune response.
Principal investigator Dr. Rebecca Porter noted that nearly two-thirds of patients had already received three or four prior lines of therapy, making a 37.5 percent objective response rate a genuinely meaningful signal. The team is now planning deeper molecular analysis to identify predictors of response and resistance, with the goal of extending benefit and tailoring future treatment to individual tumor biology. The results are set to be presented at the American Association for Cancer Research Annual Meeting in April 2024.
At Dana-Farber Cancer Institute, researchers have found something that looks like progress in one of gynecological oncology's most stubborn problems: a combination of two drugs that, working together, shrank tumors in more than a third of patients with a particularly aggressive form of endometrial cancer.
The study involved 16 heavily treated patients with serous endometrial cancer—a rare subtype that punches far above its weight in terms of lethality. Though serous cancers represent only about 5 percent of all endometrial cancers, they account for roughly 40 percent of deaths from the disease. These patients had already been through one to four rounds of prior therapy. Their options were narrowing. Into this difficult terrain, the researchers introduced mirvetuximab soravtansine, an antibody-drug conjugate, paired with pembrolizumab, an immune checkpoint inhibitor. Six of the 16 patients saw their tumors shrink. One experienced a complete response—the cancer disappeared. Five others achieved partial responses. The trial met its primary endpoint, and the results were striking enough to warrant moving forward.
The logic behind the pairing is elegant. Antibody-drug conjugates work like guided missiles: they carry a potent anti-cancer payload attached to an antibody that seeks out a specific marker on cancer cells. In this case, the target is folate receptor-alpha, or FRα, which appears on about 30 percent of serous endometrial cancers—and at particularly high levels in this subtype. Pembrolizumab, meanwhile, is an immune checkpoint inhibitor. It essentially removes the brakes from the immune system, allowing T cells to mount an attack on cancer. The problem is that checkpoint inhibitors alone tend not to work well in the microsatellite stable, mismatch repair proficient serous cancers that made up this study population. But preclinical evidence suggested something interesting: the antibody-drug conjugate might alter the immune microenvironment in ways that would allow the checkpoint inhibitor to work better, increasing T cell infiltration into the tumor and amplifying the immune response.
Dr. Rebecca Porter, the principal investigator and a medical oncologist in Dana-Farber's Gynecological Oncology Program, emphasized the significance of the response rate in this heavily pre-treated population. Nearly two-thirds of the patients had already received three or four lines of therapy. Some of the responses, she noted, were what oncologists call exceptional. Two patients remained progression-free for extended periods—one for nearly a year, another for more than 18 months. Five additional patients achieved stable disease, meaning their cancer stopped growing, at least temporarily.
What makes these results particularly noteworthy is the population. These were not treatment-naive patients with newly diagnosed disease. These were people for whom standard options had been exhausted or had failed. In that context, a 37.5 percent objective response rate—meaning measurable tumor shrinkage—represents meaningful activity. The trial was designed in two stages, with the second stage proceeding only if the first stage showed sufficient promise. The first stage met the bar for both stages, with more than four objective responses achieved.
But Porter and her team are already thinking beyond these initial results. They have observed that some patients progress more quickly than others, suggesting that not all tumors respond equally to the combination. The next phase of work will involve deeper molecular analysis—looking for genetic changes in the tumors or features of the immune microenvironment that might predict who will respond and who will resist. The goal is not just to understand why the combination works for some patients, but to find ways to extend the duration of response for those who do benefit. The results will be presented at the American Association for Cancer Research Annual Meeting in San Diego in April 2024, and the work points toward a future where treatment for this deadly cancer subtype might be more precisely tailored to individual tumor biology.
Notable Quotes
This study underscores the potential benefits of combining antibody drug conjugates with immunotherapies for this patient group.— Dr. Rebecca Porter, Dana-Farber Cancer Institute
The Hearth Conversation Another angle on the story
Why does this matter for endometrial cancer specifically? It's not the most common cancer.
That's exactly the point. Serous endometrial cancer is rare—only 5 percent of cases—but it kills disproportionately. It accounts for 40 percent of endometrial cancer deaths. So you have a small population of patients facing an extremely aggressive disease with very few good options once standard treatments fail.
And these patients had already been through multiple rounds of therapy?
Yes. Almost two-thirds had received three or four prior lines of treatment. So this isn't a study of newly diagnosed patients with lots of options left. These are people at the end of the line, in some sense. Finding a combination that works in that setting is significant.
How does the antibody-drug conjugate actually work differently from just giving chemotherapy?
It's targeted. The antibody seeks out cells expressing folate receptor-alpha—a marker on these cancer cells—and delivers the drug directly to them. That specificity matters because it can reduce damage to healthy cells. And in this case, it seems to do something else: it changes the immune environment in the tumor in ways that make the checkpoint inhibitor work better.
So the two drugs are synergistic—they enhance each other?
That's the theory, and the preclinical evidence supported it. Checkpoint inhibitors alone don't tend to work well in this type of endometrial cancer. But when you pair it with the antibody-drug conjugate, something shifts. The ADC appears to increase T cell infiltration into the tumor, which allows the immune system to attack more effectively.
What happens next? Is this going to become a standard treatment?
Not yet. This was a small, early-stage trial—16 patients in the first cohort. The next step is to understand why some patients respond and others don't. Porter's team is planning molecular analyses to identify predictors of response. If they can figure out which patients are most likely to benefit, that could inform how the treatment is used going forward.