The total number of breast cancer cases in the United States is forecast to be 50 percent greater in 2030 than it was in 2011, when invasive and in-situ or screening-detected cancers are counted together, and this increase is driven mostly by a marked increase in cases of oestrogen receptor (ER)–positive tumours and in women older than 70, according to research presented at the AACR Annual Meeting 2015, April 18-22.

“Managing this clinical burden will present a huge challenge,” said Philip S. Rosenberg, PhD, a senior investigator in the division of cancer epidemiology and genetics at the National Cancer Institute (NCI). “The one silver lining is that we expect fewer ER–negative tumours, which include the most difficult-to-treat HER2-positive and triple-negative subtypes.”

According to Rosenberg, during the next several decades, 40 million American women who were born between 1946 and 1964 will face high absolute risks for postmenopausal breast cancer, which for the average woman is estimated to be 2 percent to 4 percent over a 10-year period.

An additional 56 million women, most of them currently in their 20s and 30s, will be at substantial risk of premenopausal breast cancer, averaging 0.4 percent to 1.5 percent over a 10 year period.

With this study, Rosenberg and colleagues wanted to estimate the future incidence and burden of new cases of breast cancer according to in-situ, invasive, and ER status, in order to help the oncology community develop a proactive roadmap to optimise prevention and treatment strategies.

To do this, the researchers used nationally representative cancer surveillance data from the NCI Surveillance, Epidemiology, and End Results Program, population projections produced by the Census Bureau, and mathematical forecasting models to project the future numbers of breast cancer cases in the United States from 2011 to 2030.

Because screening mammography has been well-accepted in the United States, the researchers forecast rising numbers of both invasive and in-situ tumour diagnoses, which are almost entirely detected via screening mammography.

The total number of new breast cancer cases classified as invasive and in-situ is expected to increase by about 50 percent from 283,000 in 2011 to 441,000 in 2030.

Rosenberg and colleagues forecast that although the proportion of new breast cancer cases among women ages 50 to 69 is expected to decrease from 55 percent in 2011 to 44 percent in 2030, the proportion of cases in women ages 70 to 84 is expected to increase from 24 percent to 35 percent.

Data from the study forecast that the proportion of ER-positive invasive cancers will remain at about 63 percent; the proportion of ER-positive in-situ cancers, most of which are detected through screening mammography, will increase from 19 percent to 29 percent.

In contrast, the researchers forecast that the proportion of ER–negative cancers, both invasive and in-situ, will decrease from 17 percent of all tumours in 2011 to 9 percent in 2030.

“The reasons for this decline remain unclear, but there are intriguing clues. For example, early age at first birth in the absence of breast-feeding is a particularly strong risk factor for early onset of ER-negative tumours. We know that in recent years, women have been delaying births and breast- feeding more often, both of which might partly explain the decline in this type of breast cancer,” Rosenberg explained.

“In sum, our results suggest that although breast cancer overall is going to increase, different subtypes of breast cancer are moving in different directions and on different trajectories,” Rosenberg said.

“These distinct patterns within the overall breast cancer picture highlight key research opportunities that could inform smarter screening and kinder, gentler, and more effective treatment.”

Watch the press conference and video interview for more.

Source: AACR