MHC class II marks stronger immune response and longer survival in ovarian cancer

A new study sheds light on why some patients with the most aggressive form of ovarian cancer respond better to treatment than others. Tumors positive for a molecule called MHC class II are linked to stronger immune responses and longer survival.

These findings from a large study led by the University of Helsinki highlight how certain ovarian cancer cells can shape the immune response around them, offering clues that may help refine prognosis and future therapies.

By closely examining ovarian cancer tissue from more than 280 women, researchers discovered that patients tended to do better when immune cells gathered in groups at the edge of the tumor, where cancer meets healthy tissue. This border area turned out to be a crucial place where the body's defence tries to stop the disease from spreading.

The findings show that cancer cells can influence how the immune system behaves nearby, and that this "front line" is where the most important battles between the tumor and the body take place.

We were able to create detailed maps of over 1000 ovarian cancer tissues, zooming in on individual cells and how they are arranged. This powerful imaging approach showed that the immune system was already fighting back - we just didn't know how to see it before."

Anniina Färkkilä, study's lead researcher, specialist in gynecology, University of Helsinki

One of the most important discoveries involved a molecule called MHC class II. Normally used by immune cells to alert the body to external threats, this molecule was also found on some cancer cells. Tumors with higher levels of MHC class II were linked to stronger immune responses and more favorable outcomes, independently of traditional clinical or molecular risk factors.

These results position MHC class II as a key molecular signal linked to longer survival.

To test what this means for treatment, researchers used tumor samples grown from patients in the lab. When these tumors carried MHC class II, immune cells were better able to attack the cancer after immunotherapy. When the signal was blocked, the immune response weakened.

This suggests that immunotherapies work better for patients whose tumours express MHC class II, and that we can use MHC class II as a marker to select patients for these treatments in the clinics. Boosting MHC class II could also be a way to make patients respond to immunotherapies.

"We were surprised to see cancer cells using a signal normally reserved for the immune system," said Anniina Färkkilä. "This marker helps explain why some patients' immune systems recognize and fight their tumors more effectively, and it helps us to better treat ovarian cancer with immunotherapy in the future."

The findings, published in Cancer Discovery, a journal of the American Association for Cancer Research, on February 9, 2026, demonstrate how we can harness the immune system and apply more personalized treatment approaches in ovarian cancer.