A small group of ovarian cancers that usually resist treatment may have an unexpected weakness.
Researchers in Japan and the United States found that some clear cell ovarian tumors contain a strong inflammatory signal that appears to make them more vulnerable to immunotherapy. The key signal comes from a protein called IL-17.
The study was led by researchers at Kindai University, with collaborators from RIKEN and other institutions. The work was published in the journal Molecular Cancer. The findings may eventually help doctors identify which patients are most likely to benefit from treatments that help the immune system attack cancer.
Ovarian cancer begins in the ovaries or closely related tissues and is often difficult to detect early. Clear cell ovarian cancer is a distinct form of the disease and is especially common in Japan, where it accounts for roughly one-quarter of ovarian cancers. It can be difficult to treat after it returns because it often responds poorly to standard chemotherapy.
Immunotherapy has transformed treatment for several cancers. Some of these medicines remove the biological “brakes” that normally stop immune cells from attacking too strongly, allowing them to recognize and fight cancer cells. Unfortunately, large studies of ovarian cancer have generally shown limited benefit.
One reason may be that many clear cell ovarian tumors are considered “cold.” In simple terms, they contain relatively few active immune cells that can attack the cancer. Yet doctors have occasionally seen patients with this cancer respond very well to immunotherapy, raising an important question about what makes those tumors different.
The researchers examined tumor tissue and genetic information from 180 people with clear cell ovarian cancer. Most tumors showed little immune activity, as expected. But about 5% belonged to a small group with unusually high activity of IL-17, a protein involved in inflammation and immune responses.
These IL-17-high tumors contained more immune cells and showed signs that those cells were active. Importantly, this pattern appeared even when the tumors did not have other features doctors sometimes use to predict whether immunotherapy will work. This suggests that IL-17 activity could provide a different way to identify potential responders.
The team then used laboratory-grown cells and mice to investigate what IL-17 was actually doing. They found that IL-17 could act directly on cancer cells and switch on an internal response called NF-κB. That response caused cancer cells to release chemical signals that attracted immune cells into the tumor.
The result was a major change in the area surrounding the cancer. Instead of remaining relatively empty of immune defenders, the tumor attracted more immune cells capable of attacking cancer. In mice, this inflammatory environment made treatment with an anti-PD-L1 immunotherapy more effective and helped the animals survive longer.
Detailed analysis of individual cells also suggested that the immune cells entering these tumors were still able to fight. They had not simply gathered around the cancer without functioning properly. This helps explain why tumors with strong IL-17 activity may respond better when immunotherapy releases the immune system’s brakes.
The researchers stress that IL-17 did not simply predict whether a patient would naturally have a better outcome. Instead, it appeared more useful as a possible marker of whether immunotherapy might work. That difference is important because a treatment marker could eventually help doctors choose therapy more precisely.
The study is promising, but it is not yet a reason to change treatment for most patients. Only around 5% of the human tumors showed the strong IL-17 pattern, and much of the evidence explaining the mechanism came from cells and mouse experiments. Researchers still need clinical studies showing that patients selected using this marker truly benefit more from immunotherapy.
Another unanswered question is whether increasing IL-17 activity would be safe or useful. Inflammation can sometimes help the immune system attack cancer, but long-lasting inflammation can also damage healthy tissue and may support cancer in other situations. Any future treatment based on this pathway would therefore need careful testing.
Overall, the study offers a useful explanation for why a small number of clear cell ovarian cancers may behave differently from the majority.
If the findings are confirmed in patients, testing IL-17 activity could help prevent a one-size-fits-all approach and direct immunotherapy toward people with the best chance of responding. The larger lesson is that even cancers considered resistant to immunotherapy may contain smaller biological groups with very different treatment possibilities.
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Source: Kindai University.
