Description of study cohort and patient characteristics
Between Jan 1st, 2005 and Dec 31st, 2016, a total of 3124 women were diagnosed with MBC in the Stockholm–Gotland region, of whom 600 women were registered to have an OS of 90 days or less, thus being eligible for inclusion in the study cohort. After reviewing medical records, 102 women were excluded from the study cohort; 64 due to discrepancy in registered OS, 15 due to other active synchronous cancers, 12 due to metastasis from another primary cancer, 10 due to ongoing treatment for local recurrence or having untreated primary BC, and one due to diagnosis prior to Jan 1st, 2005. As a result, 498 women were enrolled in the final study cohort. From the control cohort, 7 patients were excluded, leaving 2581 women in the final control cohort (Fig. 1). Thus, almost one out of six women (16.2%) died within 90 days of MBC diagnosis.
The demographic and clinicopathological characteristics of the patients included in the study are summarized in Table 1. There was a significant age difference between the two groups, with a median age of 73.4 years (26.5–97.6) in the study cohort vs. 65.9 years (21.8–99.5) in the control cohort (median test p < 0.001). Patients in the study population had a higher primary disease grade compared to the control cohort (Pearson’s chi-square p = 0.001), more advanced clinical stage (Pearson’s chi-square p = 0.002), and less often hormone receptor-positive disease, with 32.7% being ER-negative in the primary setting as opposed to 18.2% in the control group (Pearson’s chi-square p < 0.001). This difference was also seen regarding PR status on primary tumor, with 49.0% being PR-negative in the study group vs. 31.4% in the control group (Pearson’s chi-square p < 0.001). No difference regarding HER2 status was detected; however, there was considerable missingness regarding HER2 data. There was no significant difference in de novo metastatic disease between the study and control cohort (16.7% versus 17.4%, Pearson’s chi-square p = 0.693). In the study cohort, 23.2% of patients for whom receptor status was available for both the primary tumor and the metastasis showed ER conversion (McNemar’s test p = 0.026), 33.7% had PR conversion (McNemar’s test p < 0.001), and 10.1% had HER2 conversion (McNemar’s test p = 1.000) (supplementary table 1).
Table 1 Demographic and clinicopathological characteristics of patients diagnosed with metastatic breast cancer in Stockholm–Gotland region 2005–2016 The most common site of metastasis in patients with short survival was CNS or viscera as opposed to bone, lymph node, or skin, which were the most common site of metastasis in all other patients (Pearson’s chi-square p < 0.001).
Treatment patterns in the metastatic setting
Of the 498 women included in the study cohort only 47.4% (n = 236) received antitumoral therapy. Systemic treatment was given to 37.8% of the women, endocrine treatment (ET) being most common (19.9%), followed by chemotherapy (17.7%). In addition, 9.6% of the included women received radiotherapy only, whereas no treatment information was available for 29 women (5.8%).
As a result, 233 women (46.8%) in the study cohort did not receive any antitumoral therapy. For 189 (81.1%) of these, no treatment recommendation was made. This was due to death during the initial work-up (n = 41), liver failure (n = 37), or poor performance status (PS)/comorbidities (n = 93). In 15 cases, no treatment recommendation was given due to patient demand. In 3 cases, the reason for a lack of treatment recommendation was unknown. Moreover, for 33 women (14.1%) recommendation was made but no treatment was administered due to death prior to treatment initiation (n = 23), poor PS (n = 6), or patient demand (n = 3). In one case, the reason was unknown. For 11 women, no information on treatment recommendation was found.
Women in the study cohort that received treatment were significantly younger than those who did not (median test p < 0.001). The presence of liver metastases was negatively associated with treatment (Pearson’s chi-square p = 0.008), whereas there was a positive association with the presence of CNS metastases (Pearson’s chi-square p < 0.001), due to a high proportion of women receiving whole-brain irradiation. There were no differences in treatment patterns according to ER status of metastatic disease (Pearson’s chi-square p = 0.307), HER2 expression at metastatic disease (Pearson’s chi-square p = 0.077), or DRFI (Pearson’s chi-square p = 0.658). However, a temporal trend toward fewer patients receiving cancer therapy in recent years was found, from 55.3% during 2005–2008 to 42.2% during 2013–2016 (Cochran–Armitage test for trend p = 0.018). This trend was significant for radiotherapy (Cochran–Armitage test for trend p < 0.001) but not chemotherapy (Cochran–Armitage test for trend p = 0.812) or endocrine therapy (Cochran–Armitage test for trend p = 0.773).
Predictors of short survival
The results of univariate and multivariable logistic regressions in respect to inclusion to the study cohort are presented in Table 2. All predictors of short survival in univariate analysis were included to the multivariable model. In multivariable analysis, five factors remained significantly associated with short survival: age, time period, metastasis site, adjuvant chemotherapy, and primary tumor grade (Fig. 2, Table 2).
Table 2 Binary logistic regression for predictors of survival < 90 days