Most patients with solid tumors develop antibodies after COVID-19 vaccination, but many patients with hematologic malignancies fail to seroconvert, according to a meta-analysis published in the European Journal of Cancer.1

The research also showed a low risk of breakthrough SARS-CoV-2 infection among cancer patients overall — less than 1%. However, cancer patients were about twice as likely as non-cancer control individuals to have a breakthrough infection after being fully vaccinated.

The meta-analysis included 35 studies that encompassed more than 8000 cancer patients in the United States, Europe, Israel, and Turkey. Most patients received the Pfizer-BioNTech COVID-19 vaccine.

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The studies, which were published between March 2020 and August 2021, reported seroconversion rates based on levels of anti-spike (anti-S) protein antibodies. Researchers also analyzed data on T-cell response and rates of SARS-CoV-2 infection after vaccination from the 6 and 14 studies, respectively, that reported these endpoints.

It is the first meta-analysis of the immune response to COVID-19 vaccination in the cancer patient population.

“Patients with cancer were not included in the main Pfizer and Moderna [COVID-19 vaccine] trials, or they were underrepresented, so you cannot draw conclusions from those,” said Bryan Vaca-Cartagena, MD, a physician at Hospital Zambrano Hellion Tecsalud in Mexico and an author of the meta-analysis. “When you do a meta-analysis, you are gathering all the findings from small studies…, and then you can get a solid conclusion that, I think, can resemble a big, randomized controlled trial.”

The meta-analysis results support the effectiveness of these vaccines, Dr Vaca-Cartagena said. He and his colleagues decided to perform the meta-analysis after conducting a survey that revealed vaccine hesitancy among patients with breast cancer in Mexico.2

Seroconversion by Cancer Type, Immunization Status

The meta-analysis showed that patients with solid tumors had consistently high rates of seroconversion after complete immunization — 94% across all the studies analyzed.1 However, 53% of solid tumor patients produced anti-S antibodies after incomplete immunization.

Among patients with a hematologic malignancy, there was a wide range in seroconversion rates across the studies. Overall, 65% of patients developed anti-S antibodies after complete immunization, and 49% developed anti-S antibodies after partial immunization.

When compared with non-cancer control individuals, patients with hematologic malignancies were 37% less likely to seroconvert after being fully immunized and 57% less likely to seroconvert after partial immunization.

Solid tumor patients had a 5% lower likelihood of seroconversion after full immunization, when compared with non-cancer control individuals. However, the cancer patients had a 55% lower likelihood of seroconversion after partial immunization.

“One of the most important findings was about the importance of completing the vaccination scheme. Even though it was not the same efficacy as in non-cancer patients, we proved that [vaccines] were efficacious and reduced the risk of getting infected with COVID-19,” said lead study author Andrea Becerril-Gaitan, MD, a physician at Hospital Zambrano Hellion Tecsalud.

The researchers were not able to assess the effects of cancer treatments on immune response to vaccination because there was not enough data across the studies included. Likewise, the researchers were not able to investigate whether certain types of solid and blood cancers were associated with lower rates of seroconversion.

“Many more studies have come out now,” and the group may consider doing another meta-analysis in a few months, said study author Ana Ferrigno, MD, also from Hospital Zambrano Hellion Tecsalud.

This article originally appeared on Cancer Therapy Advisor