From 1950 to 2000, the global incidence of lymphoma tripled, and doctors don’t know why.
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It happened in our neck of the woods too. Now joint Israeli-Palestinian research has isolated a number of risk factors involved in B-Cell Non-Hodgkin Lymphoma that had not been previously recognized – some shared by Israelis and Palestinians, some unique to each group. Non-Hodgkin lymphomas are tumors that originate in our white blood cells, either in type-B or type-T lymphocytes. The disease is responsible for about 3% of all cancer worldwide.
The scientists also confirmed a previous discovery, that people who used black hair dye manufactured before 1980 are at particular risk.
We know, says hematologist Prof. Ora Paltiel of Hebrew University-Hadassah, that B Cell Non-Hodgkin Lymphoma has both genetic and environmental components. We just don’t know what they are.
The unique opportunity afforded by this study is that Israelis and Palestinians have very close genetic backgrounds – the closest genetic cousins to Jews are Palestinians and Italians, of all people. But Israelis and Palestinians live in very different environments. It creates an opportunity to focus more sharply on environmental risk factors, Paltiel explains to Haaretz.
The result was identification of shared risk factors – and unique ones to each group, as the groups report in Plos One. Israelis and Palestinians share much genetics and the same basic ecosystem, but differ in lifestyle, health-related patterns and medical systems.
Israel, leader in lymphoma
Paltiel herself initiated the joint research because of her natural interest in cancer and particular one in this form, with its unusual growth rate. Previously, epidemiological studies of NHL had been done in the U.S. and Europe, and some on East Asian populations, but no work had been done in Middle Easterners, though the disease is common here.
As of 2012, Israel ranks first in the world in NHL incidence rates. The disease is the fifth most common malignancy in Israel and the eighth most common malignancy among West Bank Palestinians, say the scientists.
Recruiting from both the Palestinian Arab and Israeli Jewish populations, the researchers looked at medical history, environmental and lifestyle factors among 823 people with B-cell non-Hodgkin lymphoma (B-NHL) and 808 healthy controls.
The herpes factor
In both Israelis and Palestinians, tanning in sun for fun is associated with increased probability. In both, so is a history of hospitalization for infection, and having a first-degree relative with a blood cancer – of any type, not necessarily NHL itself, says Paltiel. So is using black hair dye made before 1980.
An inverse association was noted with alcohol use, but note that these results were largely based on questionnaires. (Some exposures, including smoking and greater-than-monthly indoor pesticide use, were associated with specific subtypes of B-NHL.)
But among Palestinian Arabs only, risk factors included gardening – probably because of use of pesticides, though there could be other explanations, Paltiel says.
Also uniquely to the Palestinians, another risk factor was a history of herpes, mononucleosis, rubella and blood transfusion.
Herpes, but not among the Jews? “These are soft reports,” Paltiel points out – people were asked questions such as “did you ever have herpes or the kissing disease,” and the number of positive reports among the Palestinians compared with the controls was higher than among the Israelis. All that can be concluded at his stage, Paltiel cautions, is that the Palestinians with B-NHL self-reported more exposure to herpetic infections in their own medical history of themselves.
Risk factors that applied to Israeli Jews only included growing fruits and vegetables (again pesticide, exposure?), and self-reported auto-immune diseases.
The fact is that risk factors are operating differently in different ethnic groups, which begs research into how the environment is affecting the expression of our genes. But even so, Paltiel stresses, the divergence may reflect differences in diet, cultural habits, socioeconomic, environmental and housing conditions and much more.
On the Palestinian side, participating institutions included hospitals and the Al-Quds Public Health Society. “The most important thing about the study is that it was done,” Paltiel concludes.