IV Post

Sacramento, California - The Environmental Health Investigations Branch (EHIB) of the California Department of Public Health (CDPH) conducted a follow-up investigation of pancreatic cancer cases in the Oroville area of Butte County.

Pancreatic cancer is the fourth-leading cause of cancer-related death. It is difficult to find early because it is not detectable on routine exams, and symptoms tend to be non-specific and not very noticeable until the cancer is in later stages. The average age at the time pancreatic cancer is diagnosed is 72.

The Butte County Public Health Department and EHIB sought to interview the cases in order to determine if they shared experiences or characteristics (e.g. unusual exposures, known risk factors or possible environmental/occupational factors) that might suggest why the excess occurred. There were 24 cases in the 2004 – 2005 time period, and we also included nine cases that had been diagnosed in 2006 at the time of the investigation, although reporting for that year was not yet complete, for a total of 33 cases. We were able to contact and interview 25 of these 33 cases or their next-of-kin.

Since the time the investigation was conducted, an additional case was reported that had been diagnosed in 2006. The ten cases in 2006 are fewer than the number of cases occurring in the years 2004 or 2005, but still greater than the expected number per year. However, if ten cases had occurred in 2006 without elevations in nearby years, this would not appear to be out of the ordinary.

The demographic characteristics of the group were not unusual, and typical pancreatic cancer risk factors were common, including: diabetes; family history of diabetes and cancer, particularly pancreatic cancer; and tobacco use.

Although a variety of possible environmental and occupational exposures were noted, none were consistently found among enough members of the group to explain the occurrence of the excess. For example, some members of the group reported occupations such as mechanics or welders or exposures like pesticides that may have increased their risk for pancreatic cancer. Locally caught fish were generally not eaten. Only one case had ever worked at the wood treatment facility; only two lived in an area evacuated during the fire; and the only person

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who may have consumed well water from the groundwater plume was the former worker.

Specific causes for most community cancer clusters are rarely found. If the thousands of communities in the state are considered, it is almost certain that some will have higher than normal cancer rates by chance. However, barriers that make it difficult to recognize an environmentally caused cancer excess, if one were to exist, include: the long latency period; the different exposures that can cause the same cancer; and incomplete information regarding past exposures. Cancer is not directly tied to one cause the way an infectious disease is caused by a specific bacterium or virus, and is usually caused by a combination of multiple factors.

In conclusion, we performed an extensive field investigation and data review and found no common factor among the cases that could plausibly account for an excess of pancreatic cancers. Many cases shared a known risk factor for pancreatic cancer (such as smoking, being overweight, having diabetes, or a family history of pancreatic cancer), and some worked at specific occupations that may be linked to pancreatic cancer (such as mechanic, welding, working with pesticides), but no widespread exposure or unusual Oroville circumstances appeared responsible for the community wide excess.

We recommend continued monitoring of the occurrence of pancreatic cancer for the next few years to determine if the number of cases returns to within the expected range, as is suggested by the decline in more recent data, or whether an excess persists.