Aqueous Film-Forming Foam (AFFF) & Cancer

Aqueous Film-Forming Foams (AFFFs) are specialized firefighting foams specifically designed to extinguish fires, especially those involving highly flammable liquids. They possess unique properties:^1,2,3

• Composition: On a chemical level, AFFFs are surfactants (molecules that help liquids mix by reducing surface tension, making soaps lather, and cleaning agents more effective) that have been fluorinated and hydrogenated (meaning fluoride and hydrogen have been added to their chemical structure). They are heat-resistant, non-flammable, and non-biodegradable.
• Applications: AFFFs have widespread use in firefighting, textiles, paper products, electroplating, paints, waxes, and polishes.

Historically, many AFFFs contain chemicals called PFASs (per- and polyfluoroalkyl substances).²

What are PFASs?

PFASs are human-made chemicals containing fluorine atoms bonded to a carbon chain. They are persistent and do not break down easily.

• PFAAs, a subset of PFASs, possess an acidic functional group (carboxylate or sulfonate) that enhances water mixing.
• Notably, PFOS (perfluorooctane sulfonic acid) and PFOA (perfluorooctanoic acid), present in AFFFs, are the most extensively researched PFAS compounds.²

There were some associations between the development of different types of cancer and increased exposure to chemicals found in AFFFs.⁴

• Prostate cancer
• Kidney cancer
• Liver cancer
• Colorectal cancer
• Bladder cancer
• Hematopoietic and lymphatic malignancies

PFOA and Kidney Cancer

There is strong evidence linking exposure to PFOA, found in AFFFs, to kidney cancer, based on multiple studies.⁴

• They cited 6 studies that found positive associations between PFOA and kidney cancer.^4,5
• However, one occupational study of 3M workers found no association between PFOA exposure and kidney cancer.⁶

PFOA and Testicular Cancer

Some studies have suggested an association between PFAS exposure and testicular cancer in humans.⁴ However, the evidence is limited. It can be summarized as follows:^4,7

• One cohort study showed higher testicular cancer rates with more PFOA exposure.
• A case-control study also found a positive exposure-response relationship.
• One ecological study linked higher testicular cancer rates to PFAS-exposed areas.
• A preclinical study showed that PFAS caused testicular Leydig cell tumors in rats. But Leydig cell tumors are extremely rare in humans, so the rat study has unclear relevance to human disease.

PFOA and Pancreatic Cancer

There have been no human studies yet that link PFAS to pancreatic cancer. The evidence is limited to animal and cell studies, as follows:^8,9,10

• One rat study found increased pancreatic cell proliferation after exposure to a PFAS chemical.
• Another study showed PFOA and PFOS were toxic to human pancreatic stem cells.
• Proposed biological mechanisms involve PFAS disruption of bile acid transport or stimulation of pancreatic cell growth. But the mechanisms are still hypothetical and require more research.

PFOA and Prostate Cancer

No studies have yet established a direct link between PFAAs and the development of prostate cancer in humans. However, a 2014 study did find a correlation between certain PFAAs and an increased risk of hereditary prostate cancer, as described below:²

• The study examined 201 cases of prostate cancer from 2007-2011 and measured the serum concentrations of specific perfluorinated sulfonates (PFHxS and PFOS) and carboxylates (PFOA, PFNA, PFDA, and PFUnDA).
• The main takeaway was that individuals with a family history of prostate cancer and high concentrations of certain PFAAs were at a statistically significant higher risk for the disease.
• However, it’s important to note that having a family history of prostate cancer without high concentrations of PFAAs, or having high concentrations of PFAAs without a family history, did not significantly increase the risk.

Limitations of Clinical Studies

The clinical studies reviewed had potential biases and weaknesses that limit the conclusions that can be drawn. Examples of biases and weaknesses include:⁴

• Loss of study participants during follow-up periods may cause a selection bias, in which the process of selecting individuals for a study skews the results.
• Research focusing solely on death rates may not provide comprehensive insights into non-lethal conditions, like testicular cancer. Yet, alternative approaches to identifying cases have their own drawbacks. For instance, self-reported data may not always be reliable, and the degree of inaccuracy can vary depending on the specific health outcome under consideration.
• Pre-existing health conditions or genetic factors may be present before any exposure occurred and may be over or under-represented in the study population compared to the general population.

Another study examined cancer rates in 32,254 patients from a community exposed to PFOA in drinking water, where PFOA, also prevalent in aqueous film-forming foams (AFFFs) used in firefighting, is a concerning environmental contaminant.⁵

• 2,507 total cancer cases were identified, spanning 21 different cancer types.
• Positive associations were found between PFOA exposure and kidney and testicular cancers.

However, the study had limitations, including:⁵

• Only surviving patients were included, excluding fatal cancers.
• Cancer reporting relied on patient self-reporting, which may be incomplete.
• Pre-existing conditions were not accounted for.

The use of PFOS and PFOA has raised environmental and health concerns leading to regulatory action.^2,3

• For example, environmental concerns have led to a phased-out production of PFASs by companies like 3M since 2002.
• Products containing PFOS have been banned in several European countries.
• Additionally, the use of AFFFs as fire extinguishers by firefighters has ceased.

Some lab animal studies have demonstrated a causal link between exposure to chemicals found in AFFFs and certain cancers, but the relevance to human disease is uncertain.

• For example, rats developed rare testicular and pancreatic cancers in one study.⁷ However, these specific cancers are extremely uncommon in humans.
• Cancer has a complex, multifactorial origin involving genetics, environment, and lifestyle factors making proof of causality from environmental exposure more difficult.