Significant advances in breast cancer treatment have improved care to the point where most women with an early invasive breast cancer diagnosis can expect to be survivors. A new study involved half a million women in England has found that in England, the cumulative mortality within five years of an early invasive breast cancer diagnosis has fallen from roughly 14% in the 1990s to just under 5% for women diagnosed in 2010–2015. The findings, published in The BMJ, also serve to identify the cases with the greatest risks, and point to the need for progressively larger study sizes for new treatments.
Annually, more than 2 million patients receive a diagnosis of invasive breast cancer around the world. For most, it is their first cancer. Most have early stage disease and receive surgery as their first treatment. Post-treatment outcomes vary widely across patient characteristics and countries. In order to inform treatment, follow-up and likely outcomes, more detailed mortality estimates were needed.
To address this, the researchers conducted a retrospective population based cohort study of 512 447 women, looking at diagnoses made within four time periods: 1993–99, 2000–04, 2005–09, and 2010–15. They examined annual breast cancer mortality rates and cumulative risks by time since diagnosis, calendar period of diagnosis, and nine characteristics of patients and tumours.
Across all time periods, the crude annual breast cancer mortality rate was highest during the five years after diagnosis and then declined. For any given time since diagnosis, crude annual breast cancer mortality rates and risks decreased with increasing calendar period. Crude five year breast cancer mortality risk was 14.4% for women with a diagnosis made during 1993-99 and 4.9% for women with a diagnosis made during 2010-15.
Adjusted annual breast cancer mortality rates also decreased with increasing calendar period in nearly every patient group, by a factor of about three in oestrogen receptor positive disease and about two in oestrogen receptor negative disease. Mortality rates were highest during the five years after diagnosis before declining with each following five-year period.
There was still significant difference in mortality according to individual characteristics: <3% for 62.8% of women but taking into account age, oestrogen receptor type, and the number of lymph nodes involved, among other factors, for 4.6% the risk was ≥20%.
“[O]ur findings can be used to reassure most women treated for early breast cancer that they are likely to become long term survivors” as well as to identify cases with high mortality risk, the researchers wrote in The BMJ. They also note that the reduced mortality means that future randomised controlled trials, such as for new interventions, will need to be larger in order to have sufficient statistical power.
