Lymphopenia may predict the risk of infection after radiotherapy in patients with solid tumors, according to research published in Advances in Radiation Oncology.

The researchers found that patients had a higher incidence of bacterial infection within 3 months of starting radiotherapy, and a multivariable analysis revealed an association between radiation-induced lymphopenia and bacterial infection.

“Lymphocyte counts are rarely done systematically during or after radiotherapy, but our results indicate that these provide useful information, alerting the treating physician of patients at high risk of infection,” the researchers wrote.


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For this study, the researchers evaluated the incidence of bacterial, viral, and fungal infections in patients with solid tumors in the first year after starting radiotherapy, with or without chemotherapy.

The study included 6334 patients — 2865 who received radiotherapy alone and 3469 who received radiation and chemotherapy. The most common diagnosis was breast cancer — 28.9% in the combination group and 43.2% in the monotherapy group. Other cancer types included head and neck, brain, esophageal, lung, endometrial/cervical, colorectal, and prostate cancers.

Infections by Treatment and Cancer Type

In the first year after the start of radiotherapy, there were 2104 definite infections in 1424 patients (22.5%). When the researchers considered possible or probable infections as well, there were 11,264 infections in 4450 patients (70.3%).

The incidence of definite infections per 100 patient-years was 2.76 overall, 4.26 in the first 3 months after starting treatment, and 1.81 between 9 months and 12 months after the start of treatment.

Definite infections were more frequent among patients who received chemotherapy and radiotherapy than among those who received radiotherapy alone — 23.7% and 21.0%, respectively (P =.013).

The incidence of definite infections per 100 patient-years was 2.96 among patients who received combination therapy and 2.53 among those who received radiation alone. When looking at infection incidence over time, there was only a difference between the treatment groups in the first 3 months — 4.68 in the combination group and 3.76 in the monotherapy group.

When the researchers looked at definite infections by cancer type, they found that patients with breast cancer had the lowest rate of infection in both the combination and monotherapy groups (12.7% and 9.6%, respectively).

The cancer type with the highest risk of infection was colorectal cancer among patients who received combination therapy (45.6%) and cervical or endometrial cancer (56.4%) among patients who received radiotherapy alone.

Bacterial Infections Most Common

Bacterial infections were the most common type in the combination and monotherapy groups, with incidences of 2.80 and 2.45 per 100 patient-years, respectively. The proportions of specific bacterial infections were similar between the treatment groups, and urinary tract infections were the most frequent type.

The incidence of definite bacterial infection per 100 patient-years was higher in the first 3 months after the start of radiotherapy — 4.4 in the combination group and 3.6 in the monotherapy group — and decreased over time. There were no temporal trends for definite fungal or viral infections.

In a multivariable analysis, patients with grade 3 or higher lymphopenia in the first 3 months after starting radiotherapy had a higher incidence of definite bacterial infections (incidence rate ratio, 2.66; P =.003).

“Future prospective studies should evaluate subtypes of lymphocytes compromised during radiotherapy, as well as the integrity of the immune response after radiation in specific cancer diagnosis,” the researchers concluded.

Reference

Terrones-Campos C, Ledergerber B, Specht L, Vogelius IR, Helleberg M, Lundgren J. Risk of bacterial, viral and fungal infections in patients with solid malignant tumors treated with curative intent radiation therapy. Adv Radiat Oncol. Published online March 21, 2022. doi:10.1016/j.adro.2022.100950