Cancer patients who receive an immune checkpoint inhibitor have more than a doubled rate of venous thromboembolism during the subsequent 2 years, compared with their rate during the 2 years before treatment, according to a retrospective analysis of more than 2,800 patients treated at a single U.S. center.
The study focused on cancer patients treated with an immune checkpoint inhibitor (ICI) at Massachusetts General Hospital in Boston. It showed that during the 2 years prior to treatment with any type of ICI, the incidence of venous thromboembolic events (VTE) was 4.85/100 patient-years that then jumped to 11.75/100 patient-years during the 2 years following treatment. This translated into an incidence rate ratio of 2.43 during posttreatment follow-up, compared with pretreatment, Jingyi Gong, MD, said at the virtual American Heart Association scientific sessions.
The increased VTE rate resulted from rises in both the rate of deep vein thrombosis, which had an IRR of 3.23 during the posttreatment period, and for pulmonary embolism, which showed an IRR of 2.24, said Dr. Gong, a physician at Brigham and Women’s Hospital in Boston. She hypothesized that this effect may result from a procoagulant effect of the immune activation and inflammation triggered by ICIs.
Hypothesis-generating results
Cardiologists cautioned that these findings should only be considered hypothesis generating, but raise an important alert for clinicians to have heightened awareness of the potential for VTE following ICI treatment.
“A clear message is to be aware that there is this signal, and be vigilant for patients who might present with VTE following ICI treatment,” commented Richard J. Kovacs, MD, a cardiologist and professor at Indiana University, Indianapolis. The data that Dr. Gong reported are “moderately convincing,” he added in an interview.
Dr. Umberto Campia
“Awareness that patients who receive ICI may be at increased VTE risk is very important,” agreed Umberto Campia, MD, a cardiologist, vascular specialist, and member of the cardio-oncology group at Brigham and Women’s Hospital, who was not involved in the new study.
The potential impact of ICI treatment on VTE risk is slowly emerging, added Dr. Campia. Until recently, the literature primarily was case reports, but recently another retrospective, single-center study came out that reported a 13% incidence of VTE in cancer patients following ICI treatment. On the other hand, a recently published meta-analysis of more than 20,000 patients from 68 ICI studies failed to find a suggestion of increased VTE incidence following ICI interventions.
Attempting to assess the impact of treatment on VTE risk in cancer patients is challenging because cancer itself boosts the risk. Recommendations on the use of VTE prophylaxis in cancer patients most recently came out in 2014 from the American Society of Clinical Oncology, which said that VTE prophylaxis for ambulatory cancer patients “may be considered for highly select high-risk patients.” The impact of cancer therapy on VTE risk and the need for prophylaxis is usually assessed by applying the Khorana score, Dr. Campia said in an interview.
VTE spikes acutely after ICI treatment
Dr. Gong analyzed VTE incidence rates by time during the total 4-year period studied, and found that the rate gradually and steadily rose with time throughout the 2 years preceding treatment, spiked immediately following ICI treatment, and then gradually and steadily fell back to roughly the rate seen just before treatment, reaching that level about a year after treatment. She ran a sensitivity analysis that excluded patients who died during the first year following their ICI treatment, and in this calculation an acute spike in VTE following ICI treatment still occurred but with reduced magnitude.
She also reported the results of several subgroup analyses. The IRRs remained consistent among women and men, among patients who were aged over or under 65 years, and regardless of cancer type or treatment with corticosteroids. But the subgroup analyses identified two parameters that seemed to clearly split VTE rates.
Among patients on treatment with an anticoagulant agent at the time of their ICI treatment, roughly 10% of the patients, the IRR was 0.56, compared with a ratio of 3.86 among the other patients, suggesting possible protection. A second factor that seemed linked with VTE incidence was the number of ICI treatment cycles a patient received. Those who received more than five cycles had a risk ratio of 3.95, while those who received five or fewer cycles had a RR of 1.66.
Her analysis included 2,842 cancer patients who received treatment with an ICI at Massachusetts General Hospital. Patients averaged 64 years of age, slightly more than half were men, and 13% had a prior history of VTE. Patients received an average of 5 ICI treatment cycles, but a quarter of the patients received more than 10 cycles.
During the 2-year follow-up, 244 patients (9%) developed VTE. The patients who developed VTE were significantly younger than those who did not, with an average age of 63 years, compared with 65. And the patients who eventually developed VTE had a significantly higher prevalence of prior VTE at 18%, compared with 12% among the patients who stayed VTE free.
The cancer types patients had were non–small cell lung, 29%; melanoma, 28%; head and neck, 12%; renal genitourinary, 6%; and other, 25%. ICIs have been available for routine U.S. practice since 2011. The class includes agents such as pembrolizumab (Keytruda) and durvalumab (Imfinzi).
Researchers would need to perform a prospective, randomized study to determine whether anticoagulant prophylaxis is clearly beneficial for patients receiving ICI treatment, Dr. Gong said. But both Dr. Kovacs and Dr. Campia said that more data on this topic are first needed.
“We need to confirm that treatment with ICI is associated with VTEs. Retrospective data are not definitive,” said Dr. Campia. “We would need to prospectively assess the impact of ICI,” which will not be easy, as it’s quickly become a cornerstone for treating many cancers. “We need to become more familiar with the adverse effects of these drugs. We are still learning about their toxicities.”
The study had no commercial funding. Dr. Gong, Dr. Kovacs, and Dr. Campia had no disclosures.