Having One Obesity-related Cancer Increases the Risk for Another

Data from the CPS-II Nutrition cohort showed that cancer survivors with obesity have a 78% higher risk for developing a new obesity-related cancer.

two large women walking arm in arm inside dressed in black smaller size

Credit: ECPO

The Challenge

About 20% (1 out of every 5) of all new cancer cases each year are second primary cancers—ones that are not related to the first type of cancer diagnosed. Adult cancer survivors who have overweight or obesity have a higher chance of developing a second primary cancer compared to cancer survivors without either of these conditions.

According to a 2020 American Cancer Society (ACS) study, cancer survivors with obesity have an especially higher risk of developing and dying from a second primary cancer—specifically, from a type of obesity-related cancer.

Prior adult studies have focused only on the development of second primary cancers in survivors for specific second cancers, such as survivors of female breast cancer and survivors of colorectal cancer.

Obesity-related Cancers

Everyone who develops an obesity-related cancer does not have overweight or obesity, but people who do have overweight or obesity, have a higher chance of developing one of these types of cancer with excess weight as a risk factor.

The Research

Clara Bodelon, PhD, ACS senior principal scientist of survivorship research, was the lead author of a study published in JAMA Network Open in September 2024. She and fellow ACS researchers in the Population Science team, used data from men and women who were part of the ACS Cancer Prevention Study-II (CPS-II) Nutrition cohort to learn how body mass index (BMI) is related to the incidence of a second primary cancer in adults who have a history of a cancer that hasn’t spread far from the original spot (called a nonmetastasizing cancer).

As far as the researchers know, this is the first study to evaluate the association of obesity with the risk of developing a second primary cancer using a prospective cohort study of multiple cancer survivors.

The team started with a cohort of 26,894 participants who had been diagnosed with a nonmetastatic primary cancer. The average (mean) participant was 72, almost 60% were men, 60% had overweight or obesity, and more than 95% were White.

From the Glossary for Nonscientists

Featured term: Mean

The mean, or average, is determined by adding all the numbers in a data set and dividing by the total count of numbers. For instance, here is how to determine the mean of 2, 3, 4 and 5: Add the numbers together 2+3+4+5= 14. Then divide that sum by the 4, which is how many numbers have been added together. The mean of 2, 3, 4 and 5 is 3.5.

Participants Whose First Cancer Diagnosis was Obesity-related

The most common types of first primary cancers in study participants were prostate, breast, and colorectal. Of them:

43% (11,497) had overweight (a body mass index (BMI) of 25 to less than 30)
17% (4,684) had obesity (a BMI of 30 or above)

Here’s an overview of the team’s findings:

Onset of Second Primary Cancer

About 3,750 (about 14%) survivors developed a second primary cancer. And of those second cancers, 1,243 (33%) were an obesity-related type of cancer.

The average age of people diagnosed with a second primary cancer was 77.

percentage of second primary cancers diagnosed after at least 1 year since the first cancer diagnosis

percentage of second primary cancers diagnosed after at least 5 years since the first cancer diagnosis

Increased Risk of Developing a Second Primary Cancer

Compared to cancer survivors with a normal-range BMI (18.5 to less than 25), the risk for developing a second cancer is higher for people with overweight or obesity:

15%

Increased risk for people with overweight to develop a second primary cancer

34%

Increased risk for people with obesity to develop a second primary cancer

Increased Risk of Developing an Obesity-Related Second Primary Cancer

Compared to cancer survivors with a normal-range BMI (18.5 to less than 25), the risk for developing a second obesity-related second cancer is higher for people with overweight or obesity:

40%

Increased risk for people with overweight to develop an obesity-related second cancer

78%

Increased risk for people with obesity to develop an obesity-related second cancer

How Higher BMIs affect Risk

The increased risk for developing a second primary cancer and a second obesity-related second cancer increases as BMI increases.

13%

Increased risk of developing a second cancer for every 5 point increase in BMI

28%

Increased risk of developing a second obesity-related cancer for every 5 point increase in BMI

Why It Matters

This study added to the previous knowledge that people with obesity not only have a higher risk for developing an obesity-related cancer but also for developing a second primary cancer type associated with obesity.

Since overweight and obesity are so prevalent in the United States, and especially among cancer survivors, these findings have public health implications and may inform evidence-based survivorship guidelines to reduce the risk of second primary cancers among cancer survivors and communication to physicians to heighten awareness of second cancers among cancer survivors, especially older ones and those with overweight or obesity.

For Cancer Survivors: What Else to Know About Your Risk for a Second Cancer

After reading about this research, you know that having overweight or obesity may increase your risk for developing a new type, or second, cancer. These articles give more details about risks.

Causes and Risks of Second Cancers