Is Contralateral Mastectomy Effective?

Does bilateral mastectomy for treatment of unilateral breast cancer reduce the 20-year risk of breast cancer mortality? A recent study has tried to answer this question. The study included 661,270 women (about half the population of Hawaii) with unilateral stage 0-III breast cancer who were closely matched by treatment type (lumpectomy, unilateral mastectomy, or bilateral mastectomy) and followed up for 20 years. 

The findings indicate that contralateral mastectomy for unilateral breast cancer is an effective means of cancer prevention but does not reduce the risk of dying of breast cancer. This cohort study used the Surveillance, Epidemiology, and End Results (SEER) Program registry database to identify women with unilateral breast cancer who were diagnosed from 2000 to 2019. 

During the 20-year follow-up, there were 766 contralateral breast cancers observed in the lumpectomy group, and 728 contralateral breast cancers in the unilateral mastectomy group. The cumulative breast cancer mortality was 32.1% at 15 years after developing a contralateral cancer and was 14.5% for those who did not develop a contralateral cancer. Deaths from breast cancer totaled 3,077 women (8.54%) in the lumpectomy group, 3,269 women (9.07%) in the unilateral mastectomy group, and 3,062 women (8.50%) in the bilateral mastectomy group. 

This cohort study indicates that the risk of dying of breast cancer substantially increases after experiencing a contralateral breast cancer. Women with breast cancer treated with bilateral mastectomy had a greatly diminished risk of contralateral breast cancer; however, they experienced similar mortality rates as patients treated with lumpectomy or unilateral mastectomy. 

Once again, the value of our cancer registries and the importance of aggressive patient follow-up have been shown to answer important oncological questions. 

The Importance of Modifiable Risk Factors in Cancer Prevention

A recent study led by researchers at the American Cancer Society found that four in 10 cancer cases and about half of all cancer deaths in adults aged 30 and older in the United States may be attributed to modifiable risk factors, including cigarette smoking, excess body weight, alcohol consumption, physical inactivity, diet, and infections. Cigarette smoking was by far the leading risk factor, contributing to nearly 20% of all cancer cases and 30% of all cancer deaths.

In this study, researchers utilized nationally representative data on cancer incidence, mortality, and risk factor prevalence to estimate the proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors. This analysis covered overall cancer rates (excluding nonmelanoma skin cancers) and 30 specific cancer types.

These risk factors included cigarette smoking (current and former smoking), secondhand smoke, excess body weight, alcohol consumption, consumption of red and processed meat, low consumption of fruits and vegetables, dietary fiber, and dietary calcium, physical inactivity, ultraviolet (UV) radiation, as well as infection with the Epstein-Barr virus, Helicobacter pylori, hepatitis B virus, hepatitis C virus, human herpes virus-8 (also called Kaposi sarcoma herpesvirus), human immunodeficiency virus, and human papillomavirus (HPV).

The results showed cigarette smoking had the largest population attributable fraction, or proportion of cancer cases attributable to risk factors in the population, contributing to 56.0% of all potentially preventable cancers in men and 39.9% in women. Excess body weight had the second-largest population attributable fraction (7.6%), followed by alcohol consumption (5.4%), UV radiation exposure (4.6%), and physical inactivity (3.1%).

By cancer type, the proportion of cases caused by potentially modifiable risk factors ranged from 100% for cervical cancer and Kaposi sarcoma to 4.9% for ovarian cancer, and it exceeded 50% for 19 of 30 evaluated cancer types.

The work of Oncology Data Specialists and the analysis of cancer registry data contributed to these findings' importance.

The Importance of Second Cancers

The importance of “sequence” and documentation of subsequent cancer continues to be an important aspect of cancer registry abstraction. A study from researchers at the University of Cambridge in England highlights this issue and reports that patients with breast cancer are more likely to develop a second cancer in their lifetime.

Previous studies suggested the risk of developing a non-breast second primary cancer was 24% for women and 27% for men. However, the recent study found the risk can be greater depending on the type of cancer. The study, published in April 2024, used the National Cancer Registration Dataset in the United Kingdom to analyze data from more than 580,000 women and more than 3,500 men who survived breast cancer and were diagnosed between 1995 and 2019.

Here are six findings:

1. Women who survived breast cancer had double the risk of contralateral breast cancer as the general population, and they were at 87% greater risk of endometrial cancer, 58% higher risk of myeloid leukemia and 25% greater risk of ovarian cancer.
2. Women diagnosed with breast cancer before age 50 were 86% more likely to develop a second primary cancer, whereas women diagnosed after age 50 had a 17% increased risk.
3. Women from more socioeconomically disadvantaged backgrounds were at a 35% higher risk of second primary cancer compared to those from less deprived backgrounds. The difference was driven by non-breast cancer risks, particularly for lung, kidney, head and neck, bladder, esophageal and stomach cancers.
4. Male breast cancer survivors were 55 times more likely to develop contralateral breast cancer compared to the general male population.
5. Male breast cancer survivors were 58% more likely to develop prostate cancer.
6. About 3 in every 100 men diagnosed with breast cancer at age 50 or older developed contralateral breast cancer during a 25-year period.

The documentation of subsequent cancers will be an even more critical issue in the future as the number of cancer survivors increases.