Dual battles: The ties between two cancer diagnoses, affecting 2% to 17% of patients

By Stephanie Srakocic | Fact-checked by Davi Sherman
Published January 29, 2024

Key Takeaways

  • There are multiple factors that can lead to the diagnosis of two or more primary cancers in one patient.

  • Genetics, such as the BRCA gene, can often increase the risk of multiple cancers in the same patient.

  • Additional factors, including lifestyle, medications, and previous cancer treatments, are also linked to an increased risk of multiple types and diagnoses of cancer.

The Duchess of York, Sarah Ferguson, often called Fergie, has been diagnosed with melanoma. The diagnosis is Ferguson’s second cancer diagnosis in a year; she was diagnosed with breast cancer in early 2023. In an Instagram post, Ferguson revealed that her skin cancer was discovered during breast cancer treatment.[] 

In January 2023, famed tennis star Martina Navratilova announced that she had throat and breast cancer at the same time. The cancers were discovered during the same diagnostic testing but were unrelated. Both cancers were found while in stage 1.[] 

These two high-profile stories call attention to the possibility of multiple cancer diagnoses in the same patient. A range of factors affect the likelihood of someone receiving more than one cancer diagnosis in their lifetime, but the overall occurrence of multiple primary cancers is between 2% and 17%. Some cancers have a much higher rate of being linked to a second cancer diagnosis. For instance, about 2% of people with brain and central nervous system cancers receive a second cancer diagnosis, while some 16% of people with urinary bladder cancer receive a second diagnosis.[] 

Today, about 5.4% of Americans are cancer survivors. It’s predicted that the total number of cancer survivors in the United States will increase by 24.4% by 2032. This is more cancer survivors than ever before, representing an increased pool of people with the potential to develop secondary cancers. In recent years, new understandings of cancer and its causes have started to shed light on why second cancers sometimes develop.[]

Genetic links 

Lisa Madlensky, Ph.D., CGC, a board-certified genetic counselor and program director at UC San Diego Health, says genetics can link multiple cancer types.

“The thing we’re always most concerned about is a genetic predisposition,” Dr. Madlensky says. “So, if someone is diagnosed with breast cancer and ovarian cancer, that is a sign that there is possibly a BRCA1 or [BRCA]2 mutation or a mutation on a related gene. The other major one is a woman who is diagnosed with both colon and endometrial cancer: those two go along with a condition called Lynch syndrome. They’re the two most common cancers that occur in families that have Lynch syndrome. So, anybody diagnosed with both of those should definitely have genetic testing and be evaluated for possible Lynch syndrome.” 

 The BRCA2 gene mutilation also increases the risk of inherited melanoma. The average individual is at a 1% to 2% risk for melanoma, while people with the BRCA2 gene mutation have a 3% to 5% lifetime risk. Prostate and pancreatic cancer risks are also higher for people with BRCA1 and BRCA2 gene mutations.[] []

Similarly, the inherited Peutz-Jeghers syndrome causes an increased risk of developing gastrointestinal, breast, and ovarian cancer. Li-Fraumeni syndrome increases the risk of developing bone, brain, breast, and adrenal cancer, as well as acute myeloid leukemia and soft tissue sarcoma. An inherited fault in the PTEN gene increases the risk of developing melanoma and breast, bowel, thyroid, kidney, and uterine cancer.[] 

“There are also rare genetic syndromes out there that cause rare cancers, too. There are lists and lists,” says Dr. Madlensky. 

Additional risk factors

Genetics aren’t the potential cause of a secondary cancer diagnosis. Sometimes, the risk factor that led to one cancer diagnosis can lead to another, separate cancer diagnosis. These can sometimes include lifestyle-related risk factors. For example, smoking is linked to an increased risk of developing multiple types of cancer, including lung, throat, mouth, esophagus, stomach, and liver cancer. Lack of physical activity and obesity are also linked to an increased risk of developing certain types of cancers, including breast and ovarian cancer.[] []

Additionally, the human papillomavirus (HPV) is linked to an increased risk of developing many types of cancer, including cervical, anal, vaginal, vulvar, penile, and oropharyngeal cancer. An HPV infection can lead to the same person developing separate cervical and vaginal cancer.[] 

Certain medications can increase the risk of developing multiple cancers. For instance, long-term use of hormonal oral contraceptives increases the risk of developing both breast and cervical cancer. The long-term use of immunosuppressive medications—after an organ transplant, for example—is also linked to an increased risk of developing certain types of cancer, including neck, head, lung, and skin cancers.[] 

Unfortunately, undergoing cancer treatment can also be a risk factor for developing a second cancer. Radiation therapy can increase the risk of developing some cancer types, including solid tumors (especially those that form in breast and thyroid tissue) and most types of leukemia. Some types of chemotherapy medications have also been linked with certain kinds of second cancers, including acute myelogenous leukemia and myelodysplastic syndrome.[] 

Sometimes, a linked cause or factor cannot be found. Dr. Madlensky says that people who are diagnosed with multiple cancers later in life are more likely to have unconnected causes. 

“Say a woman without a family history of cancer is diagnosed with breast cancer in her 60s. In her 70s, she receives a melanoma diagnosis, and [she] has a history of sunbathing. Those cancers are unlikely to be related and more likely to be the result of age and exposure,” Dr. Madlensky explains. “Conversely, if someone shows up in their 40s and is diagnosed with, for example, both endometrial and colon cancer, that would be a strong indicator of a linked genetic predisposition,” she says.

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