The Helsinki Criteria were established in 1997 to help doctors determine if lung cancer and other pleural diseases are asbestos-related. If a person's lung cancer is diagnosed as asbestos-related, it must fit two criteria:

The first addresses the latency period:

• Lung cancer must develop at least 10 years after initial exposure to asbestos.

Asbestos-related lung cancer has a minimum latency period of 10 years. If a person is diagnosed within a decade of his or her first exposure to asbestos, the exposure is ruled out as a possible contributing factor. If a patient developed lung cancer 10 or more years after initial exposure, they fit the first criterion. To prove that asbestos contributed to the development of lung cancer, the patient must fit only one of the remaining Helsinki Criteria:

Remaining criteria:

• Diagnosis of asbestosis.
• Higher than normal asbestos fibers in the lung tissue. The number of asbestos fibers is measured per gram of dry lung tissue and must coincide with the amount seen in asbestosis patients. The exact amount varies based on type and length of asbestos fibers.
• Higher than normal exposure to asbestos, measured in fibers per milliliter of air a year (fibers/mL-yr). The patient must have been exposed to levels of airborne asbestos equal to 25 f/mL-yr. To reach this threshold in a one-year work period, the patient must have been exposed to a level of 25 f/mL. Such a high level is typically only found in asbestos manufacturing and asbestos insulation work. To reach 25 f/mL-yr in a five-year period, an individual must have been exposed to asbestos at a level of 5 f/mL. This level is typical of shipbuilding and construction work.

In 2004, researchers reviewed new study results that had emerged since the Helsinki Criteria first were formed. Researchers concluded the 17-year-old criteria still held. But they amended the list to answer a common question.

Researchers more closely considered the role of smoking in asbestos-related lung cancer, stating that a second cause of cancer complicates the issue. Most lung cancer cases are linked to smoking, and some are further linked to asbestos. The authors are careful to note the secondary attribution is difficult to determine. Because asbestos and smoking work together synergistically, researchers suggest it is especially difficult to distinguish smoking-related cases from those caused by both smoking and asbestos.

The Helsinki Criteria at work: Suppose a man is diagnosed with lung cancer and worked as a shipbuilder 30 years earlier for several years. The individual fits the first criterion: his first exposure to asbestos was more than 10 years before his diagnosis. He also fits one of the remaining criteria: his occupation exposed him to asbestos at a level of at least 25 f/mL-yr. Because of these two risk factors, doctors would conclude that asbestos caused or contributed to the man's lung cancer.

The main critique of the Helsinki Criteria is a result of contradictory hypotheses relating asbestos exposure to lung cancer.

There are three distinct and conflicting hypotheses about asbestos exposure causing lung cancer:

• Asbestos exposure only increases the risk of lung cancer when it has caused asbestosis.
• Asbestos exposure increases the risk of lung cancer when it is enough to cause asbestosis, despite whether it actually led to an asbestosis diagnosis. This is the hypothesis favored by the Helsinki Criteria.
• Asbestos exposure always increases the risk of lung cancer, absent of any threshold needed for asbestosis.

The Helsinki Criteria specifically state that asbestosis is not necessary to prove a causal relationship, but that asbestosis must have been possible based on the amount of exposure. Researchers who disagree with this hypothesis disagree with the Helsinki Criteria. Proponents of the first hypothesis argue the criteria are too lenient, and supporters of the third hypothesis argue they are too strict. Despite some opposition, the Helsinki Criteria are an accepted standard throughout the world.

Countries struggling with asbestos-related health problems lay out their own versions of the Helsinki Criteria. Panels of experts worldwide typically accept the Helsinki Criteria as a valid set of guidelines and make minor changes specific to each country. The American Thoracic Society (ATS) lays out criteria to determine if a disease is caused by asbestos. The ATS states that, although its guidelines are outlined for nonmalignant diseases and not lung cancer, they coincide with the Helsinki Criteria.

The AWARD (Adelaide Workshop on Asbestos-Related Diseases) Criteria, another set of widely recognized standards, was laid out in 2000 to determine the utility of the Helsinki Criteria in Australia. In making the AWARD Criteria, Australia's experts made minor alterations to reflect the specific types of asbestos found in the country. Overall, the panel of experts deemed the Helsinki Criteria to be reasonable and applicable.

Asbestos-Related Lung Cancer and Asbestosis: After much debate, the medical community now believes the presence of asbestosis is a reliable diagnostic marker that a patient has received enough asbestos exposure to develop lung cancer. Some studies claimed asbestosis must be present for lung cancer to be associated with asbestos, while others stated the two can exist independently. Asbestosis and lung cancer are commonly associated because the risk for both rises in a parallel manner as asbestos fibers accumulate in lung tissue. Evidence shows the level of exposure required to develop asbestosis and lung cancer is similar.