Inflammatory and other breast cancer incidence rate trends by estrogen receptor status in the Surveillance, Epidemiology, and End Results database (2001-2015).

Purpose: Inflammatory breast cancer (IBC) rates increased in the United States before the turn of the twenty-first century. We examine trends by estrogen receptor (ER) status since then.

Methods: Using data from the Surveillance, Epidemiology, and End Results (SEER) program for years 2001-2015, we calculated age-adjusted incidence rates for IBC (defined by AJCC TNM category T4d, extent of disease codes, and morphology code 8530) by ER status, which was imputed if unknown, among women aged 25-84 years. For comparison, we included other locally advanced breast cancer and other breast cancers partitioned into localized and regional/distant/unstaged. We fit joinpoint log-linear models to annual rates to calculate annual percentage change (APC) and average annual percentage change (AAPC).

Results: The rate of increase in ER+ IBC rates among women aged 25-44 (AAPC = 0.5) was similar to other advanced tumor types, but declines among women aged 45-84 (AAPC = - 2.2) were more rapid. Declines in ER- IBC rates for women aged 25-84 (AAPC = - 3.7) were more rapid than for other tumor types.

Conclusions: Our results show a reversal of the rising rates of IBC overall reported at the end of the twentieth century. Direction of trends for IBC is consistent with other breast cancer types, except for ER+ localized breast cancer in older women. Decreasing parity and rising prevalence of older age at first birth may contribute to declining rates of ER- IBC. Otherwise, patterns of changing risk factors are inconsistent with the trends we observed. Further studies of IBC are necessary to identify additional risk factors and possible preventive strategies.