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Though metastatic breast cancer survival is improving, rates vary by region



Though survival rates of patients with metastatic breast cancer (MBC) have increased over the last 2 decades, a new study has indicated disparities exist across regions and by variables like age and race.

“It appears from these results that we may be at a crossroads for MBC treatment and survival,” wrote Judith A. Malmgren, PhD, of the University of Washington and her coauthors. The study was published in Cancer. “Access to appropriate, timely, and up‐to‐date diagnosis, care, treatment, and surveillance could turn this fatal disease into a chronic and treatable phenomenon, depending on patient factors, molecular subtype, and insurance capacity to pay for treatment,” they said.

To determine how breast cancer outcomes might vary across regions, the researchers compared breast cancer–specific survival rates (BCSS) from Surveillance, Epidemiology, and End Results-9 (SEER-9) registry data minus a regional subset from the Seattle-Puget Sound (S-PS) region (n = 12,121) to patients from that S-PS region (n = 1,931) and to an individual cohort in that area (n = 261). Five-year BCSS rates were calculated for three time periods: 1990‐1998, 1999‐2004, and 2005‐2011.

All analyzed patients were diagnosed with a first primary, de novo, stage IV breast cancer between the ages of 25 and 84 years from 1990 to 2011. Patients in the SEER-9 group and the S-PS region had a mean age of 61 years, compared with the individual cohort’s mean age of 55 years. Patients in the individual cohort were more likely to reside in a major metropolitan area of over 1 million people, compared with the SEER group and the S-PS region (86% versus 61% and 58%, respectively).

Patients in the SEER-9 group had improved BCSS rates over the study period, from 19% in 1990-1998 (95% confidence interval, 18%-21%; P less than .001) to 26% in 2005-2011 (95% CI, 24%-27%; P less than .001). Patients in the S-PS region saw even greater improvements in BCSS rates, from 21% in 1990-1998 (95% CI, 18%-24%; P less than .001) to 35% in 2005-2011 (95% CI, 32%-39%; P less than .001). But the largest improvement in survival rates came from patients in the individual cohort, who went from 29% in 1990-1998 (95% CI, 18%-37%; P less than .001) to 56% in 2005-2011 (95% CI, 45%-65%; P = .004).

In a proportional hazards model for breast cancer–specific death, reduced hazard in the SEER-9 group was associated with surgery (hazard ratio, 0.58; 95% CI, 0.55-0.61; P less than .001), an age less than 70 (HR, 0.77; 95% CI, 0.73-0.82; P less than .001) and white race (HR, 0.84; 95% CI, 0.79-0.89; P less than .001). Similar associations were seen in the S-PS region with surgery (HR, 0.57; 95% CI, 0.50-0.66; P less than .001) and an age less than 70 (HR, 0.72; 95% CI, 0.62-0.84; P less than .001), but not white race.

The study results “indicate that the stage IV population that is living longer may be benefiting from many of the same therapies used to treat early breast cancer, especially for patients who are able to handle adjuvant chemotherapy treatment and are HR‐positive,” the researchers said. “However, the lag in survival improvement across different population‐based, geographic regions suggests that some groups and regions may benefit unequally from treatment advances as well as timely diagnosis.”

The study was funded by the Kaplan Cancer Research Fund, the Metastatic Breast Cancer Alliance, and the Surveillance, Epidemiology, and End Results Cancer Surveillance System program of the National Cancer Institute. The authors reported no conflicts of interest.

SOURCE: Malmgren JA et al. Cancer. 2019 Oct 22. doi: 10.1002/cncr.32531.

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