Compared to the average person, breast cancer survivors with a BRCA mutation were much more likely to develop cancer in the opposite breast (called contralateral breast cancer by doctors). They were also more likely to develop ovarian, colorectal, pancreatic, and endometrial cancers.

Compared to female survivors without a BRCA mutation, women with a mutation were more likely to develop cancer in the opposite breast, as well as ovarian, colorectal, and pancreatic cancers.

Compared to male survivors without a BRCA mutation, men with a mutation were more likely to develop cancer in the opposite breast, as well as prostate cancer.

What the results mean for you
If you’ve been diagnosed with breast cancer and know you have a BRCA mutation, the results give you more detailed information about your risk of developing a second cancer. This can help you and your doctor develop a more frequent cancer screening plan that is specially tailored to your situation and preferences. It can also help you make decisions about other steps you might want to take to reduce your risk, including prophylactic mastectomy and prophylactic ovary removal.

About the study
The study included 25,811 females and 480 males who had been diagnosed with breast cancer between 1995 and 2019. More than 81% of the people were white and more than 67% were first diagnosed with breast cancer when they were younger than 45. All the people in the study had genetic testing.

Overall, 3,671, or about 14%, had a BRCA mutation:

1,840 women had a BRCA1 mutation

7 men had a BRCA1 mutation

1,750 women had a BRCA2 mutation

74 men had a BRCA2 mutation

The people were followed until Dec. 31, 2020.

The researchers compared estimated rates of second primary cancers in people with a history of breast cancer and a BRCA mutation and people in the general population, most of whom haven’t been diagnosed with cancer and don’t have a BRCA mutation.

Detailed results
Compared to people in the general population, people with a BRCA mutation were more likely to develop cancer in the opposite breast, as well as other non-breast cancers.

Women with a BRCA1 mutation were:

15.6 times more likely to develop cancer in the opposite breast

44 times more likely to develop ovarian cancer

4.8 times more likely to develop colorectal cancer

3.03 times more likely to develop pancreatic cancer

2.92 times more likely to develop endometrial cancer

1.98 times more likely to develop lung cancer

Women with a BRCA2 mutation were:

16.8 times more likely to develop ovarian cancer

7.7 times more likely to develop cancer in the opposite breast

5.72 times more likely to develop pancreatic cancer

1.62 times more likely to develop lung cancer

1.4 times more likely to develop colorectal cancer

1.36 times more likely to develop endometrial cancer

Women with a BRCA1 mutation who were first diagnosed with breast cancer at age 45 or younger were 23.5 times more likely to develop cancer in the opposite breast than women who were diagnosed at this age and didn’t have the mutation. Women who were older than 45 when first diagnosed were 9.31 times more likely to develop cancer in the opposite breast. Age at first diagnosis didn’t seem to affect risk in women with a BRCA2 mutation.

Men with a BRCA2 mutation were:

431 times more likely to develop cancer in the opposite breast

20.2 times more likely to develop pancreatic cancer

4.46 times more likely to develop prostate cancer

Compared to survivors without a BRCA mutation, survivors with a BRCA mutation were much more likely to develop a second primary cancer.

Women with a BRCA1 mutation were:

33 times more likely to develop ovarian cancer

3.6 times more likely to develop cancer in the opposite breast

2.93 times more likely to develop colorectal cancer

1.45 times more likely to develop a non-breast or ovarian cancer

Women with a BRCA2 mutation were:

12 times more likely to develop ovarian cancer

3.56 times more likely to develop pancreatic cancer

2.4 times more likely to develop cancer in the opposite breast

Men with a BRCA2 mutation were:

13.1 times more likely to develop cancer in the opposite breast

5.61 times more likely to develop prostate cancer

There was no information on men with a BRCA1 mutation in the paper. This was probably because there were only seven men with this mutation.

Source : https://www.breastcancer.org/research-news/survivors-with-brca-mutation-higher-second-primary-risk