The analysis of data from 102 patients in Israel who were undergoing cancer treatments and 78 healthy controls found that 90% of the cancer patients were seropositive for SARS-CoV-2 antispike IgG antibodies after their second vaccine dose, as compared to 100% of the controls, according to the report published in JAMA Oncology.
Although median IgG titers in the cancer patients who responded to the vaccine were significantly lower than those of the controls, antibody levels were "adequate," the researchers found.
The new study shows "even if you are getting anti-cancer treatment, (you should) get the vaccine," said study coauthor Dr. Salomon Stemmer, a clinical professor of oncology and head of the Research Unit at the Davidoff Center at the Rabin Medical Center and the Sackler Faculty of Medicine at Tel Aviv University.
Even though cancer patients had lower titers than controls, those who have seroconverted should be able to behave like vaccinated members of the general population, Dr. Stemmer said in an email.
Whether these patients would benefit from a third dose of the vaccine to boost antibody titers, "time will tell us," Dr. Stemmer said.
To take a closer look at the effectiveness of mRNA vaccines in cancer patients currently receiving treatment, Dr. Stemmer and his colleagues recruited cancer patients as well as a convenience sample of family members and caregivers who accompanied the patients when they came in for their treatments.
Between February 22, 2021 and March 15, 2021, blood samples were drawn from the study participants. Samples collected from the cancer patients were drawn before they received their antineoplastic treatment that day.
In the patient group, the median age was 66 and 57% were men, while the median age of the controls was 62 and 68% were women. Among the patients, the most common tumor type was gastrointestinal (28%), followed by lung (25%), and breast (25%).
The most common anticancer treatment was chemotherapy alone (29%), followed by immunotherapy alone (22%), and chemotherapy plus biological therapy (20%).
The median IgG titer in patients (1,931 AU/mL) was statistically significantly lower than in the control group (7,160 AU/mL). Factors such as age, gender, and type of cancer were not significantly associated with lower titers.
In a multivariable analysis, the only variable that was significantly associated with lower IgG titers was treatment with chemotherapy plus immunotherapy, the authors note.
Further study is needed to understand the clinical relevance of the lower antibody titers and how long the immune responses last, but the data suggest it's worthwhile to make vaccinating cancer patients a priority, the study team concludes.
"This is a very interesting paper," said Dr. Fred Hirsch, a professor of medicine at the Icahn School of Medicine at Mount Sinai and executive director of the Center for Thoracic Oncology at the Mount Sinai Health System in New York City. "And I'm impressed they have generated a paper within three weeks."
"Of course, the matter is urgent," Dr. Hirsch said. "We know that in cancer patients infected with COVID, there is a very high mortality rate. The mortality rate for those with lung cancer is 26% or even higher."
It's going to be important to determine why cancer patients have such a high mortality rate when infected with SARS-CoV-2, Dr. Hirsch said.
"There are several question marks related to these results," Dr. Hirsch said. "Point one is what effect is from the cancer itself and what is from the cancer treatment? Point two is, what is an adequate antibody response when it comes to protection from the virus? We don't know at this stage."
"My next question is what to do with those patients who eventually do not respond adequately, Dr. Hirsch said. "I think that needs to be a focus in the future. Do they need a boost of the same vaccine? Or two boosts of the same vaccine? Or a boost of another vaccine? And what will be the timeline for the boost?"
Dr. Hirsch hopes to be able to answer some of those questions with a Mount Sinai study of vaccinated cancer patients. "We are running a prospective study of a large cohort, 1,000 lung cancer patients, and we are studying the magnitude of the of the antibody response. We are following those patients at three, six, 12, and 24 months to see the duration of their antibody response."
SOURCE: https://bit.ly/3frSPyG , https://bit.ly/3vwLeV4 and https://bit.ly/2SDnoZ2 JAMA Oncology, online May 28, 2021.
By Linda Carroll
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