Diffuse large B-cell lymphoma (DLBCL) patients exposed to pesticides on the job have worse overall survival (OS) and event-free survival (EFS) and are less likely to respond to treatment, according to new findings.

"This study suggests for the first time, to our knowledge, a poorer prognosis for patients with DLBCL exposed to pesticides, concerning the response to treatment, 2-year EFS, and OS," Dr. Pascale Fabbro-Peray of Nimes University Hospital in France and colleagues conclude in JAMA Network Open, online April 19. "These findings must be confirmed in further prospective studies."

Pesticide spray. Soure: Getty

Pesticides and other substances used in agricultural labor have been linked to non-Hodgkin lymphoma (NHL), the authors note. DLBCL is a type of NHL characterized by an aggressive course, and accounts for roughly 30% of all NHL cases.

Dr. Fabbro-Peray and colleagues hypothesized that long-term occupational exposure to pesticides would induce cellular adaptations that could render chemotherapy less effective.

To investigate, they conducted a retrospective cohort study in 244 patients with DLBCL treated at six different hospitals in France. Sixty-seven (27.4%) study participants had occupational exposure, including 38 from agriculture, 16 from green spaces maintenance, 15 from wood activities and 11 from hygiene activity.

The authors used the French job exposure matrix (JEM) PESTIPOP to gauge the likelihood and reliability of pesticide exposure.

Treatment failed in 35 patients (14.3%), including four (1.6%) who died from chemotherapy toxicity.

Overall, two-year EFS was 78% and two-year OS was 90%. Occupational exposure was associated with significantly increased risk of treatment failure (22.4% vs. 11.3% for unexposed individuals; adjusted odds ratio, 3.0), while patients with exposing agricultural occupations were at even greater risk (29.0% vs. 11.7%, aOR, 5.1).

Two-year EFS was 70% in the occupationally exposed group, and 82% for the unexposed group (adjusted hazard ratio, 2.2; P=0.005); it was 56% for patients who worked in exposing agricultural occupations versus 83% for those who did not (aHR, 3.5; P<0.001).

Two-year OS was 81% in those with agricultural exposure and 92% in those without such exposure (aHR, 3.9; P<0.001).

The risk of treatment failure rose with the probability of pesticide exposure, particularly agricultural, the researchers note. "This finding suggests that resistance to treatment could be provided by specific agents used in farming activities," they suggest.

One drawback of the study, the authors note, is that occupational history was assessed retrospectively.

"Another limitation was the consideration of pesticides as a cocktail of all different insecticides, fungicides, and herbicides used in farming, wood, hygiene, or green space activities as one homogeneous exposure for 40 years," they add. "Many different agents have been used, and another analysis of the results with PESTIMAT (a crop exposure matrix) could give more precise details on the effects of single agents."

SOURCE: https://bit.ly/2Xw5uEW

JAMA Netw Open 2019.