Clinical Edge Journal Scan Commentary: Recent Trials in Breast Cancer, June 2022

Erin Roesch, MD

A subset of patients with HR+ metastatic breast cancer (mBC) may have primary resistance to endocrine therapy (ET), and the majority will develop progressive disease and secondary resistance at some point during their treatment course. The phase 3 PEARL trial randomly assigned 601 postmenopausal patients with HR+/HER2- mBC that was resistant to prior aromatase inhibitor therapy to capecitabine or palbociclib + ET (with exemestane or fulvestrant). There was no significant difference in OS between the palbociclib + ET and capecitabine arms in both the wild-type– ESR1 population (median OS 37.2 vs 34.8 months; adjusted HR 1.06; P = .683) and overall population (median OS 32.6 vs 30.9 months, adjusted HR 1.00; P = .995) ( Martin et al ). The randomized phase 2 Young-PEARL trial demonstrated a progression-free survival (PFS) benefit with palbociclib + exemestane + leuprolide vs capecitabine among 189 premenopausal women with HR+/HER2- mBC and relapse or progression on prior tamoxifen therapy (median PFS 20.1 vs 14.4 months; HR 0.659; P = .0235). ² In this study, half of the patients were treatment-naive in the metastatic setting and had no prior aromatase inhibitor exposure. Considering the similar survival outcomes seen in PEARL in postmenopausal patients, the choice of therapy should include consideration of other variables, such as side effects, comorbidities, and OS results, which will be further informative in the premenopausal population.

Poorer outcomes associated with breast cancer in younger women (< 45 years of age) are driven by multiple factors, including delayed diagnosis, more aggressive biologic subtypes, and advanced stage at presentation. Survival outcomes for breast cancer diagnosed and treated during pregnancy are similar to nonpregnant patients. Postpartum breast cancer (PPBC) is a distinct entity, defined as breast cancer that is diagnosed within the first 5 years after childbirth, and is more likely to have inferior outcomes. A pooled data set from the Colorado Young Women Breast cohort and the Breast Cancer Health Disparities study (n = 2519 cases) showed that among women diagnosed at < 45 years, those who were nulliparous had better OS vs those with PPBC (HR 0.61), with a more prominent effect among stage I breast cancers (HR 0.30) and in very young women diagnosed at ≤ 35 years (HR 0.44) ( Shagisultanova et al ). At 15 years of follow-up, among very young women diagnosed at ≤ 35 years, those with PPBC had an OS of 63% compared with 71% for nulliparous women and 67% for women who had given birth more than 5 years ago. There are various factors that likely contribute to poorer outcomes seen with PPBC, including mammary gland involution and a lactation effect. Research efforts focused on aspects, such as the tumor immune microenvironment in the postpartum state, lactation studies, and perhaps identification of a postpartum signature, will enhance our understanding with the goal to optimize outcomes for young women with PPBC. ^[3]

The treatment of male breast cancer in the advanced or metastatic setting is largely extrapolated from female studies. Registry data have shown differences in clinicopathologic characteristics between metastatic male breast cancer (mMBC) and metastatic female breast cancer (mFBC). For example, there is a higher proportion of simultaneous lung and bone involvement and a lower proportion of HER2+/HR- triple-negative subtypes, and simultaneous bone and liver metastasis in mMBC vs mFBC. ⁴ An analysis including 207 male patients with breast cancer with bone metastases in the Surveillance, Epidemiology, and End Results (SEER) database demonstrated 3-year OS and cancer-specific survival (CSS) rates of 36.7% and 39.5%, respectively. Inferior OS and CSS were associated with age > 60 years (for OS: HR 1.671; P = .014; for CSS: HR 1.806; P = .009), triple-negative subtype (for OS: HR 3.029, P = .003; for CSS: HR 3.025, P = .004), and lack of surgery (for OS: HR 1.746; P = .012; for CSS: HR 1.734; P = .023), whereas brain metastasis had a worse OS (HR 2.045; P = .028) but not CSS ( Zhou et al ). These findings highlight the importance of getting a better understanding of mMBC disease biology and the opportunity to tailor treatment approaches for this population of patients.

Additional References

1. Waks AG, Desai NV, Li T, et al. A prospective trial of treatment de-escalation following neoadjuvant paclitaxel/trastuzumab/pertuzumab in HER2-positive breast cancer. NPJ Breast Cancer. 2022;8:63. Doi: 10.1038/s41523-022-00429-7
2. Park YH, Kim TY, Kim GM, et al; Korean Cancer Study Group (KCSG). Palbociclib plus exemestane with gonadotropin-releasing hormone agonist versus capecitabine in premenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer (KCSG-BR15-10): A multicentre, open-label, randomised, phase 2 trial. Lancet Oncol . 2019;20(12):1750-1759. Doi: 10.1016/S1470-2045(19)30565-0
3. Lefrère H, Lenaerts L, Borges VF, et al. Postpartum breast cancer: mechanisms underlying its worse prognosis, treatment implications, and fertility preservation. Int J Gynecol Cancer. 2021;31:412-422. Doi: 10.1136/ijgc-2020-002072
4. Xie J, Ying YY, Xu B, Li Y, Zhang X, Li C. Metastasis pattern and prognosis of male breast cancer patients in US: a population-based study from SEER database. Ther Adv Med Oncol. 2019;11:1758835919889003. Doi: 10.1177/1758835919889003