Although the use of postmastectomy radiation therapy (PMRT) increased among older women with high-risk breast cancer after the initial release of evidence-based guidelines, progress lagged between 1999 and 2005, suggesting the need for additional research to better bridge the gap between clinical evidence and practice, according to a study published in the July edition of Cancer.

From 1999 to 2002, a series of evidence-based guidelines recommending PMRT were disseminated. The guidelines were based on three trials demonstrating that PMRT decreased locoregional recurrence and improved survival among high-risk women, shared Shervin M. Shirvani, MD, of MD Anderson Cancer Center in Houston, and colleagues.

The researchers hypothesized that the promulgation of the guidelines would result in increased receipt of PMRT by high-risk older women, but would not impact low- to intermediate-risk women.

Their study leveraged the Surveillance, Epidemiology and End Results (SEER) Medicare database to identify women older than age 66 who underwent mastectomy for invasive breast cancer between 1992 and 2005.

Shirvani et al devised a cohort of 38,332 women from the database and selected receipt of PMRT as their primary study outcome.

Women were stratified into low-risk (T1/T2 N0), intermediate-risk (T1/T2 N1) and high-risk (T3/T4 and/or N2/N3) groups. A final group was comprised of high-risk patients ages 66 to 79 years with absent or mild comorbidity.

According to the researchers, 23,126 women fell into the low-risk group, 7,211 into the intermediate-risk group, and 7,995 into the high-risk group. Receipt of PMRT was strongly associated with risk, wrote Shirvani, as 6.6 percent of low-risk patients, 16 percent of intermediate-risk patients and 48.5 percent of high-risk patients received PMRT.

Shirvani and colleagues also reported that PMRT use was relatively stable among low-risk patients from 1992 to 2005. “For intermediate-risk patients, PMRT increased linearly from 10.2 percent in 1992 to 21 percent in 2005.”

Among high-risk women, PMRT use did not change from the first quarter of 1992 through the second quarter of 1996. PMRT use rose significantly from 36.5 percent from the second quarter of 1996 through the second quarter of 1998 to 57.7 percent. However, from the second quarter of 1998 to the end of the fourth quarter 2005, PMRT use did not change among high-risk women, despite the dissemination of clinical guidelines supporting its use during this period.

The authors identified several factors linked with omission of PMRT among high-risk women: advanced age, moderate to severe comorbidities, smaller size tumors, absence of lymph node involvement, ductal histology, no T4 component and omission of chemotherapy.

“Our observations demonstrate the failure of evidence-based guidelines to satisfy their intended goal of summarizing and disseminating clinical evidence to everyday practice,” wrote Shirvani and colleagues.

The researchers suggested that several factors may be related to the omission of PMRT among high-risk women. These include: PMRT may have been appropriately contraindicated in some women and patients may have encountered a lack of access to RT.

However, they emphasized, “The median survival for the high-risk patients in our study who survived the first year of their cancer diagnosis and did not receive PMRT was 4.5 years, suggesting that there is a subset of patients who are not currently receiving PMRT but whose life expectancy is long enough to derive at least a locoregional control, if not overall survival, benefit from PMRT.”

Shirvani and colleagues pointed to the need for additional research to better explain the gap between evidence-based guidelines and clinical practice. They speculated that accountability measures may improve compliance.

They suggested three tactics: tying accreditation to guidelines adherence, tracking compliance via National Quality Forum quality measures and financial incentives from payors.