Breast cancer is the most diagnosed cancer in women.1 One study found that in the 10 years following their initial breast cancer diagnosis, around 10% of patients are diagnosed with a second primary cancer.2 However, less is known about what factors, such as type of cancer treatment, might contribute to the development of these second primary cancers.
To better understand how breast cancer and second primary lung cancer might be correlated, we studied 2,071,295 women aged 50–84 who received a screening mammogram between 2010 and 2023. Patients with an elevated breast cancer risk as evidenced by a previous breast or lung cancer diagnosis, a screening less than three months prior, or starting screening mammograms prior to age 50 were excluded. We assessed the rate of primary lung cancer in the five years following the screening mammogram among patients who received a breast cancer diagnosis and compared it with the rate of lung cancer in patients who did not receive a breast cancer diagnosis. We found that the five-year risk of lung cancer was doubled in the patients with breast cancer compared to those without, as shown in Figure 1.
We then further stratified the breast cancer population by the type of treatment received following the breast cancer diagnosis. Patients who received multiple forms of treatment are included in each category. We found that breast cancer patients who received chemotherapy were the most likely to be diagnosed with subsequent primary lung cancer compared to breast cancer patients who received radiation or endocrine therapies, as shown in Figure 2. A sensitivity analysis using a Cox proportional hazards model yielded similar results.
These findings suggest that patients diagnosed with breast cancer are at an increased risk of developing second primary lung cancer. Additional monitoring, such as lung cancer screening, may be warranted in patients with a previous history of breast cancer, especially if previous treatment included chemotherapy.
