Diabetes status may influence long-term survival in metastatic breast cancer

Long-term overall survival (OS) in patients with metastatic breast cancer (MBC) may be influenced by diabetes status, according to a retrospective study presented at ENDO 2022.

“Specifically in longer-term survivors, diabetes and poor glycaemic control were associated with worse survival,” noted study author Dr Y.M. Melody Cheung from the Brigham and Women’s Hospital, Harvard Medical School in Boston, Massachusetts, US.

“Our findings suggest that in patients with breast cancer who have a relatively good prognosis despite their cancer diagnosis, a more proactive management of blood sugar may lead to a longer lifespan,” she said.

Cheung and co-authors used the databases from the Brigham and Women’s Hospital and the Dana-Farber Cancer Institute, Boston, Massachusetts, US, to identify 488 patients diagnosed with MBC between January 2010 and January 2021. Diabetes status of the patients, determined as ICD 9/10 code for diabetes, HbA_1c ≥6.5 percent, or random blood glucose (RBG) ≥200 mg/dL and documented use of glucose-lowering agents, was ascertained through The Research Patient Data Registry. The 244 patients with diabetes (median age 57.6 years) were propensity score-matched by age, sex, and ethnicity with 244 patients (median age 56.6 years) without the above-mentioned diabetes criteria (control group).

Patients were primarily White (84.4 and 83.6 percent of diabetes and control cases, respectively), and had hormone receptor-positive, HER2-negative disease (61.5 and 63.5 percent, respectively). Over the study period, patients with diabetes had worse glycaemic control* than those without diabetes (median RBG 123 vs 100 mg/dL; median HbA_1c 6.6 percent vs 5.5 percent; p<0.001 for both comparisons).

OS rates at 5 years did not significantly differ between patients with and without diabetes (54 percent vs 56 percent; p=0.65). Time to next treatment, defined as the time interval between transition from a first-line metastatic therapy to a second-line regimen due to disease progression, at 1 year also did not differ between groups (56 percent each; p=0.33). [ENDO 2022, abstract RF28 | PSUN185]

Subgroup analysis showed that OS at 5 years and TTNT at 1 year also did not differ between groups based on glycaemic levels.

However, landmark subgroup analysis among patients who survived ≥8 years following MBC diagnosis showed that at 10 years, OS rates were lower among patients with diabetes than without diabetes (67 percent vs 87 percent; p=0.047), as well as among those with poor compared with good glycaemic control (63 percent vs 83 percent; p=0.018).

“There is evidence suggesting that diabetes confers worse outcomes in individuals with breast cancer,” said Cheung. “[However,] no studies have specifically evaluated this association in MBC populations.”

“These data provide some reassurance that diabetes and poor glycaemic control may not be a major contributor to overall mortality or cancer progression in most individuals with MBC,” she continued. “These findings are important as they suggest that diabetes treatment and blood sugar goals should be tailored specifically to patients even with advanced cancer based on their projected prognosis.”

“As the clinical impact of diabetes may only be felt over a longer period of time, active management of glycaemic control may be most relevant for patients who have better prognosis. Individualized diabetes goals and strategies, taking into account patient prognosis, should therefore be considered in patients with MBC,” Cheung concluded.

Cheung pointed out that the potential effect of glycaemic control on breast cancer outcomes in patients with diabetes is still unestablished. “In some instances, blood sugar control may not be strongly pursued by doctors, especially in cases where the cancer is advanced, and strict diabetic control may be considered overly burdensome for patients. A link between poor blood sugar control and worse cancer outcomes may modify the way doctors treat diabetes in patients with advanced breast cancer,” she concluded.