Radiotherapy for Lymphoma as a Risk Factor for Malignant Mesothelioma

People who received radiotherapy for the treatment of lymphoma have a higher chance of developing malignant mesothelioma later in life.

That is the conclusion of a large, population-based study of American lymphoma patients over four decades.

A Closer Look at the Data

Using data from the US Surveillance, Epidemiology, and End Results (SEER) database, researchers at Stanford Cancer Center and scientific consulting firm Exponent, Inc. identified 47,219 patients diagnosed with Hodgkin’s lymphoma and 252,090 patients diagnosed with non-Hodgkin’s lymphoma between 1973 and 2014.

The researchers then used a standard data analysis tool to determine what percentage of irradiated and non-irradiated patients later developed malignant mesothelioma.

“Mesothelioma risk was increased among HL and NHL patients treated with radiotherapy but not without radiotherapy,” states the report in Cancer Causes and Control.

Radiotherapy as a Mesothelioma Risk Factor

For most people who develop pleural or peritoneal mesothelioma, exposure to asbestos – either at work or in their environment – is the primary cause. But the new report found that mesothelioma developed in 28 of the lymphoma patients who had undergone radiotherapy and 59 who had not.

After adjusting for other factors associated with mesothelioma risk, the researchers determined that radiotherapy was an independent risk factor for second primary mesothelioma, especially in lymphoma patients diagnosed before 1995.

In addition, the more time that had passed since a lymphoma patient’s radiotherapy, the more likely they were to develop mesothelioma as a result of it. Patients who were diagnosed and received radiation at younger ages, faced the highest mesothelioma risk.

Mesothelioma Risk Still Low After Radiotherapy

Scientists have long known that exposure to radiation can also cause cellular changes that increase the risk of eventually developing malignant mesothelioma. Clinicians use extensive precautions to limit the amount of radiation absorbed by tissue outside the treatment area, but there is almost always some spillover.

Even so, the chance of developing mesothelioma still remains very low, even among irradiated cancer patients.

A 2016 Italian analysis of the SEER database concluded that malignant mesothelioma is only slightly more common in cancer patients who have had radiation than it is in the general public. Among the 935,637 patients analyzed by University of Bologna researchers, 301 were later diagnosed with mesothelioma, primarily the pleural variety.

Not surprisingly, cancer patients who lived the longest after radiotherapy treatment had the highest risk for mesothelioma. This is also the case with asbestos-induced mesothelioma, which can take decades to develop.

Sources:

Chang, ET, et al, “Therapeutic radiation for lymphoma and risk of second primary malignant mesothelioma”, July 28, 2017, Cancer Causes and Control, Epub ahead of print

Farioli, A, “Radiation-induced mesothelioma among long-term solid cancer survivors: a longitudinal analysis of SEER database”, February 10, 2016, Cancer Medicine