The question of whether asbestos exposure can cause cancer in the throat has a nuanced answer. The scientific consensus is that asbestos is a known human carcinogen, and evidence strongly links it to cancer of the larynx, which is often referred to as voice box cancer. However, the evidence is less conclusive for cancer of the pharynx, which is the upper part of the throat. This difference is rooted in the distinct anatomy of the throat and how asbestos fibers interact with these tissues.
Defining the Scope of Laryngeal and Pharyngeal Cancer
The term “throat cancer” includes cancers arising from two primary anatomical areas: the larynx and the pharynx. The larynx, or voice box, is a structure composed of cartilage, muscles, and ligaments located just below the pharynx and at the top of the trachea. Cancers in this area are termed laryngeal cancer.
The pharynx is the hollow tube that begins behind the nose and goes down to the neck, comprising the nasopharynx, oropharynx, and hypopharynx. Cancers in this area are broadly classified as pharyngeal cancer. The distinction between the larynx and pharynx is particularly important because scientific studies have revealed differing levels of evidence for a causal link to asbestos for each site.
The larynx is lined partly with respiratory-type epithelium, while the pharynx is predominantly lined with squamous cells, like the mouth and esophagus. This difference in cell type and tissue structure may contribute to the varying susceptibility of these two adjacent regions to the effects of inhaled or swallowed asbestos fibers.
Established Cancers Caused by Asbestos Exposure
Asbestos is classified by the International Agency for Research on Cancer (IARC) as a Group 1 carcinogen. This classification is based on sufficient evidence linking asbestos exposure to several specific malignancies. The most widely known and strongly linked cancer is mesothelioma, a rare and aggressive cancer of the protective linings of the lungs and abdomen.
In addition to mesothelioma, asbestos exposure is a recognized cause of lung cancer. The World Health Organization (WHO) and IARC also classify cancers of the ovary and the larynx as established outcomes of asbestos exposure. This means the evidence for an association between asbestos and laryngeal cancer is considered sufficient and causal by leading health organizations.
The risk of these cancers increases with the duration and intensity of asbestos exposure, with many cases appearing decades after the initial contact. While other cancers have been investigated, the evidence supporting a definitive causal link for them is not as strong as it is for the four established cancers.
The Journey of Asbestos Fibers to the Throat
Asbestos fibers primarily enter the body through inhalation, where their aerodynamic characteristics determine where they deposit within the respiratory tract. Shorter, thicker fibers tend to be deposited in the upper respiratory tract, including the larger airways. The body’s natural defense mechanism, known as the mucociliary escalator, then works to clear these deposited fibers.
This escalator is a layer of mucus and tiny, hair-like cilia that constantly sweep foreign particles upward toward the pharynx. Once the fibers reach the pharynx, they are typically swallowed. This process represents a secondary exposure route for the gastrointestinal tract and the pharynx.
While most swallowed fibers pass through the digestive system and are excreted, a small number may penetrate the lining of the stomach or intestines. This physical transport mechanism explains how asbestos fibers, initially inhaled, can directly contact the tissues of the pharynx and the larynx, presenting an opportunity for carcinogenic interaction.
Scientific Evidence Linking Asbestos to Throat Cancer
For laryngeal cancer, a strong and consistent association with asbestos exposure has been demonstrated across numerous epidemiological studies. Meta-analyses of both cohort and case-control studies have shown a significantly increased risk of laryngeal cancer in individuals with occupational asbestos exposure.
In highly exposed workers, the risk of developing laryngeal cancer can be more than double that of unexposed individuals, and the risk appears to be dose-dependent, increasing with the intensity and duration of exposure. This robust evidence led to the classification of laryngeal cancer as a cancer caused by asbestos by major international health bodies.
For pharyngeal cancer, however, the evidence is not as definitive, and the link is considered suggestive rather than sufficient to infer causality. Some studies have indicated a positive association, showing an elevated risk of pharyngeal carcinoma in asbestos-exposed men, but this evidence is limited compared to the data for the larynx. The IARC notes a positive association between asbestos and pharynx cancer.