Challenges of Cancer Spatial-Epidemiology
Malignancies present with long induction period, and the causative agents may disappear or biodegrade from the environment prior to malignancies detection. The identification and detection of cancer in excess in well-defined geographic area is indicative of cancer clusters. However clusters confirmation does not imply environmental causal factors, but association between geography and the said malignancy. Clusters remain feasible to confirm if rare tumors such as pediatric thyroid cancer is observed in excess in a certain geographic locale.
Causal inference while extremely difficult to achieve following clusters identification and confirmation, involves assessment of current and past potential causative agents. Therefore the search for potential insulting or causative agent/s must recognize the fact that such agents may never be found due to long induction period of malignancies and the possibility of biodegradation of malignancy-inducing substances from the environment. With such challenges, one should not solely depend on a single epidemiologic investigation to establish causal mechanism in cancer clusters. Therefore replication of studies remains a feasible approach to causal inference establishment following cancer clusters identification and confirmation.