Studying risk factors for cancer in Mexico: Q&A with Martin Lajous, MD, ScD

March/April 2024 | Volume 23 Number 2

The photo shows Dr. Martin Lajous wearing a navy suit, blue shirt and red tie.

Photo courtesy of ESMaestrasDr. Martin Lajous

Martin Lajous, a medical doctor and epidemiologist, became a researcher at Instituto Nacional de Salud Pública (INSP), Mexico’s National Institute of Public Health, in 2004. At INSP he helped design and develop the Mexican Teachers’ Cohort (MTC) and now serves as its principal investigator. MTC has since become part of the U.S. National Cancer Institute’s (NCI) Cancer Cohort Consortium. Lajous has conceived and taught courses at INSP on cancer epidemiology, causal inference (methodologies and strategies that allow researchers to draw causal conclusions based on data), and implementation science.

How did you become aware of aflatoxin exposure in Mexico?

Aflatoxin is a proven Group 1 carcinogen (causing cancer in humans), according to the WHO. This toxin comes from two fungi, Aspergillus flavus and Aspergillus parasiticus. Aflatoxin often contaminates crops like maize, a staple food in Mexico, during harvest, processing, and storage. Yet aflatoxin was completely under the radar in Mexico.

I was initially funded by NCI to do a project evaluating research needs in Mexico and Mesoamerica. One of our U.S. collaborators mentioned that liver cancer was becoming an important health priority, particularly for Hispanic populations. He asked, What's going on in Mexico? We conducted a descriptive analysis of liver cancer mortality in Mexico and identified a unique epidemiological pattern. First, areas with large rural populations had a higher burden. A striking second finding was that men and women were at equal risk of dying from liver cancer, whereas in studies done elsewhere, men were shown to be three times more at risk than women. We also saw that common risk factors for liver cancer were less ubiquitous in Mexico.

Now we knew from an NCI group working in Guatemala, the country with the highest burden of liver cancer on the continent, that aflatoxin was an important factor. So, working with this group and a colleague from Johns Hopkins, we took 100 samples from the Mexican National Health and Nutrition Survey—a representative sample of adults living in Chiapas—and sent them to Baltimore to be evaluated. We found that the prevalence of detectable levels of aflatoxin was 86%. By comparison, using the same technique on NHANES data from the U.S., the prevalence is less than 1%. (The National Health and Nutrition Examination Survey is designed to assess and track the health and nutritional status of adults and children in the United States. This unique survey, which began in the 1960s, combines interviews and physical examinations.)

So, we found that, basically, aflatoxin exposure is commonplace in Mexico likely due to contamination of maize mainly in the form of tortillas. However, as toxicologists will tell you, the issue is not exposure, per se, but the level of exposure. Fortunately, we found the levels were not as high as reported in Guatemala. We also did an analysis to detect aflatoxin-associated mutations in liver tumors and found a prevalence approaching 20%. A recent NIH-funded analysis on close to 1,000 participants conducted in five states along the Gulf Coast—Tamaulipas, Veracruz, Campeche, Chiapas, and Yucatan, all high liver cancer burden areas— confirmed our previous results, 92% of adults had detectable levels of aflatoxin.

What are your other projects in Mexico?

Mexico has a rapidly increasing burden of colorectal cancer—it’s the second leading cause of cancer mortality in the country. After characterizing the epidemiology of colorectal cancer, we began looking at barriers for implementing a colorectal cancer screening program in Mexico City. I obtained some seed funding from the Prevent Cancer Foundation, which turned out to be my project for NCI's dissemination and implementation science research training program. That experience was transforming—I saw how implementation science can help accelerate the adoption of evidence-based interventions in Mexico.

Developing a colorectal cancer screening program in Mexico became one of my career goals. Over the past five years I have collaborated with researchers experienced in colorectal cancer screening program development through the University of California, San Francisco (UCSF)-Mexico Cancer Initiative sponsored by the Global Cancer Program at the Hellen Diller Family Comprehensive Cancer Center. With them, we designed and evaluated the feasibility of a screening program in an integrated health system in Monterrey in northern Mexico, an area with high colorectal cancer burden.

This brings us to LISTOS—a 5-year, $5 million NCI grant given to UCSF, INSP, the Mexican National Cancer Institute (INCan), and UTHealth Houston. LISTOS (Leveraging Implementation Science To Optimize Strategies) for Cancer Control aims to develop a regional center that will be part of a wider network of implementation science centers funded by NCI in low- and middle-income countries. The center includes two cancer control implementation science research projects, one focused on developing a colorectal screening program, the other focused on speeding up the time between diagnosis and treatment for breast cancer patients. I lead the colorectal cancer project, and Dr. Karla Unger, a colleague from INCan leads the breast cancer project.

Tell us about the Mexican Teachers Cohort.

The person who first hired me to work at INSP said that he’d been talking to Dr. Walter Willett who at the time was the chair of the department of nutrition at the Harvard T.H. Chan School of Public Health. They thought it was a good time for Mexico to develop a large cohort to study cancer—cancer in general and breast cancer specifically. Previous efforts, unfortunately, had not been successful. So, I became involved in identifying an appropriate population and developing institutional relations to set up a cohort.

We focused on teachers for various reasons. The majority of teachers in Mexico had participated in economic incentive programs, which required yearly evaluations, so they’d become very accustomed to filling out bubble questionnaires and could self-report lifestyle and health information. That's one reason. The second reason is that federal and state educational authorities could advocate for study participation and efficiently support the distribution of questionnaires through existing channels for communication. A third reason is that most teachers had job stability, and, as government employees, all of them have access to health care through a limited number of public providers, which gives us access to their health records and ensures we’ll be able to follow them for a long time.

So, with support from the American Institute for Cancer Research the cohort began in 2006–2008 when 115,000 women responded to our baseline questionnaire. We send questionnaires every three to four years to update their health status and lifestyle factors.

MTC is the largest cancer cohort in Latin America, so it has and will provide important information on a region that's completely understudied. Globally, most cancer cohorts are in European and American populations, with some in Asian populations, so it’s an important addition to NCI's global cadre of cohorts. Our results will likely be informative for Hispanic populations living in the U.S., where there is limited prospective information on cancer risk factors and occurrence. After many years waiting for the maturation of the cohort, we will soon publish our first paper on breast cancer incidence and there are more to come.

What's ahead for you?

I’m most interested in strengthening public health. I'm focused on cancer because it’s an increasing burden in Mexico, in part because of the aging of the population, but also because of a rapid transition towards lifestyles and reproductive patterns that are more like high-income countries. There's still a lot of work to be done in descriptive epidemiology of the burden of different cancers and their risk factors. And etiologic research, looking into the origins of the disease, will help us understand how we can mitigate the population risk for breast and liver cancers in Mexico.

Implementation science is something that we in low- and middle-income countries need to consider because these methods will allow us to adapt and rapidly adopt interventions that have been effective in other populations into our clinical and public health practice. We need to bring the benefits of research to patients, their families and their communities as fast as we can. Implementation science is a way to do that. I aim to advance implementation science in Mexico by generating a platform—the infrastructure, the training—for investigators and other researchers that will allow them to conduct implementation science in Mexico and bring benefit to our communities in an effective and efficient way.