The link between environmental agents and childhood cancer is not a new concept. Environmental causes of childhood cancer have long been suspected by many scientists but have been difficult to pin down, partly because cancer in children is rare and because it is difficult to identify past exposure levels in children, particularly during potentially important periods such as pregnancy, in-utero, or even prior to conception. Hence, many of the environmental agents hypothesized for childhood leukemia remain speculative [1-3].

In this issue of Indian Pediatrics, Rau et al. [4] investigated the presence of endosulfan in the bone marrow of children with hematological malignancy residing in areas sprayed with the pesticide (in South India). This is a case-control study in which the authors report its presence in the bone marrow of 7/34 children residing in these areas including 6 who had leukemia.

The authors themselves point out that this study does not in any way prove that endosulfan is a cause of leukemia. As of date, there are no available epidemiological studies linking endosulfan exposure specifically to cancer in humans. It is important to understand that an association between an exposure and cancer does not necessarily mean that the exposure causes cancer. Most importantly, other possible explanations of the observed association must be ruled out. The consistency of an association is to be considered, and the association must be temporally correct meaning that we must be sure that the exposure actually preceded the development of the disease, which in this case would include events taking place before birth, during conception, embryogenesis and early postnatal life. Another important aspect in such a study is the sample size and whether it is truly representative of the population. As acknowledged by the authors, the small sample size, other compounding factors like genetic susceptibility, exposure to other carcinogens and their effects, are the limitations of this study.

Endosulfan,　an　off patent　organochlorine　insecticide and　acaricide　was developed in the early 1950s and has been used globally in agriculture to control insect pests.　 Although industrialized nations have restricted or banned many organochlorine pesticides, some of these chemicals (like endosulfans) are still used, on the assumption that they pose little threat to the environment, wildlife, or human health.

It has long been recognized that leukemia is a heterogenous disease with a multifactorial and multistep pathogenesis with a fetal origin being postulated by some [3,5]. Epidemiological evidence suggests that ionizing radiation, certain chemicals (such as benzene), viruses (human T-cell leukemia/lymphoma virus type I, Epstein­Barr virus), and bacteria (Helicobacter pylori) may play a part in the development of some subtypes of leukemia and lymphoma in adults and children.

Finding causes of any disease is usually a long, slow process. No one study is likely to prove that a particular exposure definitely causes a particular cancer. However, each well designed and well executed study with adequate sample size will bring us closer to understanding the causes of these cancers within populations of children.

Competing interests: None stated; Funding: Nil.

1. Pearce MS,　Hammal DM,　Dorak MT,　McNally RJ, Parker L. Paternal occupational exposure to pesticides or herbicides as risk factors for　cancer　in children and young adults: a case-control study from the North of England. Arch Environ Occup Health. 2006;61:138-44.

2. UK Childhood Cancer Study Investigators. Childhood cancer and residential proximity to power lines. Br J Cancer. 2000;83:1573-80.

3. Toren A, Rechavi G, Ramot B. Pediatric cancer: Environmental and genetic aspects. Ped Hematol Oncol. 1996;13:319–31.

4. Rau A, Coutinho A, Avabratha KS, Rau AR, Warrier RP. Pesticide (endosulfan) levels in the bone marrow of children with hematological malignancies. Indian Pediatr. 2012;49:113-7.

5. Wiemels JL, Cazzaniga G, Daniotti M, Eden OB, Addison GM, Masera G, et al. Prenatal origin of acute lymphoblastic leukaemia in children. Lancet. 1999; 354:1499–1503.