According to the World Health Organization, the disease we call “cancer” refers to a large group of diseases that arise when abnormal cells begin to grow uncontrollably and move beyond their usual boundaries to invade adjoining parts of the body and/or spread to other organs. Cancer can arise in virtually any tissue of the body. It is the 2nd leading cause of death in the world with the most common cancers being breast, lung, colon, rectum, and prostate cancers. Health systems in low- or middle-income countries are the least prepared to handle the cancer burden of their population, and, unfortunately, many patients in these systems do not have access to timely diagnostic or treatment options.
In 2019, breast, lung, and colorectal cancer accounted for the top 3 cancer burdens in the world. The table below compares these cancer incidences globally, in the US, and in Harris County, which includes the city of Houston. We can see that in 2019 the US incidences were greater than the global incidences for both breast and lung cancer. Additionally, compared to the global and US incidences, cancer incidence rates for all 3 cancers were higher in Harris County, indicating there is work to be done in the public health sector to explore the cause of these rates.
Various factors can increase an individual’s risk of developing certain cancers. These factors include genetics, physical carcinogens such as radiation, chemical carcinogens such as tobacco, and biological carcinogens such as viruses, bacteria, parasites, etc. Our exposure to these carcinogens is largely influenced by the environment in which we live. Outdoor and indoor air pollution are known risk factors that have been linked to certain cancers. Radon for example is produced from the natural decay of uranium which can slowly accumulate in buildings, houses, schools, etc. Long-term radon exposure has been associated with lung cancer. A “Cancer cluster” is a well-known term that is often associated with environmental exposures. The CDC defines a cancer cluster as a greater-than-expected number of cancer cases that occur within a group of people in a certain geographic area over a period of time. However, because cancer is a multifactorial disease, cancer clusters are often hard to address and identification of one seldom indicates a single external environmental cause for the cluster. Additionally, investigations of clusters are often cumbersome and take years to conduct. Thus, local and state health departments are charged with the task of analyzing case rates in an area and identifying any potential exposure to minimize the risk of cancer.
Environmental exposures have been researched and linked to certain cancers on a global scale. Air pollution is associated with an increased risk of mortality in breast, liver, and pancreatic cancer. A 2016 study conducted in Hong Kong looked at long-term exposure to fine particulate matter known as PM2.5 that came from pollutants produced by various sources such as transportation and power generators. The study followed subjects for 10 years and ultimately concluded that for every 10 micrograms per cubic meter of increased PM2.5 exposure, there was an overall 22% increased risk of dying from cancer. Additionally, there was an 80% increase in the mortality risk of breast cancer and a 36% increase in the mortality risk of lung cancer. The researchers concluded that pollution exposure potentially causes defects in DNA repair, suppresses the body’s immune response, or causes inflammation that leads to angiogenesis (formation of new blood vessels) allowing tumor growth.
Houston is the 4th largest city by population in the US and one of the most diverse cities in the entire nation. Houston residents are all but accustomed to environmental issues. In August 2022, an article published by the Houston Chronicle detailed the use of creosote (a chemical with carcinogenic properties) and other toxic chemicals used to treat wood for railroad construction in the railyard located in Houston’s Fifth Ward and its link to increasing cancer rates in the neighborhood. These toxic chemicals seep into the soil and groundwater. Normally, this would not be concerning as the water consumed in this neighborhood does not come directly from the ground. However, on hot days, toxic chemicals from this practice are released into the atmosphere, and researchers subsequently found that certain cancer rates increased in the area as a result. The Fifth Ward neighborhood is a predominantly Black neighborhood and historically an impoverished area in the city of Houston. It is no coincidence that this neighborhood was adversely affected by railroad construction practices, as marginalized and poor populations are often historically victims of exploitation that leads to detrimental health outcomes. These findings ultimately led Harris County, the city of Houston, and The Bayou City Initiative, a non-profit organization dedicated to environmental policy, to sue the company responsible for the contamination.
For the full story, here are some links below:
Because of these events, the Houston Health Department named the Kashmere Gardens Union Pacific Railroad site a cancer cluster in the city of Houston. The link below provides a timeline of actions taken by the Houston Health Department on analyses of the area and actions taken to clean up.
The map below was constructed by the Houston Health Department using data collected by the Texas Department of State Health Services (DSHS) in a cancer cluster analysis they completed in March 2020. It shows the geographical locations of the census tracts analyzed and highlights the ones that show significantly increased rates of certain types of cancer, including three census tracts which are located within Kashmere Gardens.
When we talk about a public’s risk of developing cancer, there are many risk factors we cannot change. We can’t change our genetics, we can’t change our age, we can’t change our family history. But we can and must change environments that put populations at unnecessary and unfairly increased risk of poor health. We believe, as global citizens, one of our collective aims should be to reduce health-related disparities and make access to health-promoting resources more equitable across boundaries. Protecting and advocating for underserved populations in our city or across the world should be a priority so that we can provide a healthy environment to future generations. Air is universal across the world and what we add to it as a process of globalization and industrialization is of paramount importance to prevent chronic disease and cancer. Public awareness, environmental protection, close monitoring, and policy change should be developed to ensure that the effects of carcinogens are minimized on the human race across the world. This is our attempt to raise awareness related to cancer clusters due to environmental causes.