Understanding the Decline in Breast Cancer Mortality: The Role of Screening and Advancements in Treatment

I have recently read an interesting study from the USA that looked at breast cancer mortality rates from 1975 to 2019.

This study found a substantial decline in breast cancer deaths for women aged 30 - 79 years in the USA. The age-adjusted mortality rate went down from 48 in 100,000 women in 1975 to 27 in 100,000 women in 2019. This is thanks to better breast cancer treatments and screening programs.

The Cancer Intervention and Surveillance Modelling Network (CISNET) used computer models to understand how treatment affects breast cancer death rates. These models looked at the impact of screening mammography, stage I to III therapy, and reductions in breast cancer mortality. Additionally, the models were updated to evaluate the influence of recent treatments for metastatic breast cancer on mortality rates.

Looking at the data in more detail showed how much each approach helped. Stage I to III treatment was found to account for approximately 47% of the reduction. Metastatic treatment played a substantial role as well, accounting for 29% of the mortality reduction. Screening contributed 25% to the reduction in breast cancer mortality. Screening accounts for the largest proportion of breast cancer mortality reduction in ER−ve/Her2-ve breast cancer, where treatment has the least advanced. However, the absolute contribution of screening to mortality reduction persisted, showing that patient who did not have their cancer diagnosed by screening had worse outcomes.

The study also examined the impact of treatment on different subtypes of breast cancer based on ER/ERBB2 (Oestrogen and Her2) status. It was found that screening had the greatest relative component of mortality reduction for ER−/Her2− breast cancer, accounting for 40% of the reduction. On the other hand, improvement in treatment had the smallest relative component for ER−/Her2− breast cancer, representing 19% of the total mortality reduction. These variations highlight that not all breast cancer is the same and that there is a need for tailored treatment approaches based on specific cancer characteristics.

In addition to assessing mortality rates, these models incorporated the event of metastatic recurrence to estimate survival measures. The models revealed that the median breast cancer-specific survival after a diagnosis of metastatic recurrence in 2019 was approximately 3.2 years, regardless of the ER/Her2 status. However, survival varied depending on the subtype, with ER+/Her2+ breast cancer having the longest median survival of 4.9 years and ER−/Her2− breast cancer having the shortest median survival of 1.6 years. The best improvement in survival rates were in Her2+ve breast cancers due to improvements in treatments for the Her2+ve metastatic breast cancer, like Herceptin and other Her2 medications.

In the UK, age adjusted mortality rate from breast cancer was 53 per 100,00 in 1975 and 33 per 100,000 in 2018. The New Zealand numbers from Te Whatu Ora (the only ones I can find) are 26 per 1000,000 in 1975 and 16.3 per 100,000 in 2018 which seems so much lower than in UK and USA, I am not sure why this is the case. We do not know how much of the improvements treatment or screening has led to this level of decrease. Still, I would expect that we would have similar if not better improvements due to screening, and possibly slightly less due to treatments as we do not have all the medications available in NEw Zealand as they do in the USA.

This study highlights the significant role of advancements in treatment, as well as the impact of screening programs. It also shows that the sooner we diagnose Er-ve/Her2-ve disease, the higher the likelihood of survival, as treatment in this group has not significantly increased survival rates. These variations highlight the heterogeneity of breast cancer and the need for tailored treatment approaches based on specific tumour characteristics. It also highlights the need for improvements in treatment for patients who have Er-ve/Her2-ve disease.