Natural killer cells deserve their name. Unlike T cells, which need prior exposure to a specific target to mount an attack, natural killer cells destroy virus-infected and early cancerous cells without any priming. They are the innate immune system's first responders. When PUFAs disarm them, the immune surveillance that normally catches tumors early falters.

The Yale team also found that engineering the LRP5 receptor without its functional LDLa binding domain—or removing LRP5 altogether—made natural killer cells better at killing tumors, both in living mice and in cell cultures.

A second pathway, a second cancer type

The Yale work echoes a March 2025 study from Weill Cornell Medicine in New York City. That team found that linoleic acid, an omega-6 fatty acid abundant in seed oils such as soybean and safflower oil and present in pork and eggs, accelerates tumor growth in triple-negative breast cancer—a hard-to-treat subtype.

In that study, linoleic acid activated a major growth pathway by binding to a protein called FABP5, which is particularly abundant in triple-negative tumor cells but not in hormone-sensitive subtypes. Mice with triple-negative breast cancer that ate a linoleic acid-rich diet developed tumors markedly faster.

Together, the two studies show that PUFAs can fuel cancer through more than one signaling route: one pathway disarms immune cells, another directly accelerates tumor growth.

"This discovery helps clarify the relationship between dietary fats and cancer, and sheds light on how to define which patients might benefit the most from specific nutritional recommendations in a personalized manner," said Dr. John Blenis, senior author of the Weill Cornell study and the Anna-Maria and Stephen Kellen Professor of Cancer Research.

"Given the widespread promotion of polyunsaturated fatty acids as beneficial dietary supplements, greater public awareness of their potential unintended effects is warranted," Luan wrote.

Important caveats

These results are preliminary. Both studies were preclinical, carried out in mice and cell cultures, and the findings may not translate directly to humans. Nothing here suggests that healthy people should abandon fish, nuts, or vegetable oils, whose cardiovascular and cognitive benefits remain well documented. The open question is how these fats behave in patients with active cancer, particularly those receiving immunotherapy.

Luan and colleagues call for further research into what controls LRP5 expression across different cancer types, which could expose new drug targets. In the long run, they argue, a better understanding of how individual diets interact with tumor immunity could pave the way for precision nutrition—tailored dietary advice for patients undergoing cancer therapy rather than one-size-fits-all recommendations.

Until then, the paradox stands: the same fats celebrated for protecting the heart may, in the context of cancer, hand tumors an advantage. It is a reminder that even "healthy" nutrients can act differently depending on the disease, the tissue, and the person.