CCNE1 and PLK1 Mediate Resistance to Palbociclib in HR+/HER2- Metastatic Breast Cancer.

PURPOSE: In hormone receptor-positive (HR+)/HER2- metastatic breast cancer (MBC), it is imperative to identify patients who respond poorly to cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) and to discover therapeutic targets to reverse this resistance. Non-luminal breast cancer subtype and high levels of CCNE1 are candidate biomarkers in this setting, but further validation is needed. EXPERIMENTAL DESIGN: We performed mRNA gene expression profiling and correlation with progression-free survival (PFS) on 455 tumor samples included in the phase III PEARL study, which assigned patients with HR+/HER2- MBC to receive palbociclib+endocrine therapy (ET) versus capecitabine. Estrogen receptor-positive (ER+)/HER2- breast cancer cell lines were used to generate and characterize resistance to palbociclib+ET. RESULTS: Non-luminal subtype was more prevalent in metastatic (14%) than in primary tumor samples (4%). Patients with non-luminal tumors had median PFS of 2.4 months with palbociclib+ET and 9.3 months with capecitabine; HR 4.16, adjusted P value < 0.0001. Tumors with high CCNE1 expression (above median) also had worse median PFS with palbociclib+ET (6.2 months) than with capecitabine (9.3 months); HR 1.55, adjusted P value = 0.0036. In patients refractory to palbociclib+ET (PFS in the lower quartile), we found higher levels of Polo-like kinase 1 (PLK1). In an independent data set (PALOMA3), tumors with high PLK1 show worse median PFS than those with low PLK1 expression under palbociclib+ET treatment. In ER+/HER2- cell line models, we show that PLK1 inhibition reverses resistance to palbociclib+ET. CONCLUSIONS: We confirm the association of non-luminal subtype and CCNE1 with resistance to CDK4/6i+ET in HR+ MBC. High levels of PLK1 mRNA identify patients with poor response to palbociclib, suggesting PLK1 could also play a role in the setting of resistance to CDK4/6i.

Symptom cluster of emotional distress, fatigue and cognitive difficulties among young and older breast cancer survivors: The mediating role of subjective stress.

OBJECTIVES: To examine the nature of the symptom cluster of emotional distress, fatigue, and cognitive difficulties in young and older breast cancer survivors (BCS); To assess the mediating role of subjective stress and coping strategies (emotional control and meaning-focused coping) in the association between age and symptom cluster. MATERIALS AND METHODS: Participants were 170 BCS, stages I-III, 1-12 months post-chemotherapy, filled-out the Fatigue, Emotional Control, Meaning-focused Coping, Emotional Distress and the Cognitive Difficulties Questionnaires. Statistical analyses included tests for difference between-groups Pearson correlations and Structural Equation Modeling for the assessment of the study model. RESULTS: Older BCS (aged 60-82) reported lower levels of emotional distress (M = 0.87, SD = 0.87), fatigue (M = 3.85, SD = 2.38), and cognitive difficulties (M = 1.17, SD = 1.07) compared to the younger BCS (aged 24-59) (emotional distress M = 1.17, SD = 0.85, fatigue M = 5.02, SD = 2.32, and cognitive difficulties M = 1.66, SD = 1.23, p < .01-,05). The older survivors reported lower levels of subjective stress and used more emotional control strategies compared to the younger BCS. The empirical model had good fit indices (χ2 = 27.60, p = 0.20, χ2/df = 1.26; CFI = 0.98; TLI = 0.98; NFI = 0.95; RMSEA = 0.04 (90% CI = 0.00, 10) and showed that subjective stress, but not coping strategies, mediated the effect of age on symptom cluster severity. CONCLUSIONS: Lower levels of subjective stress, but not coping strategies, mediated the association of age with the symptom cluster of emotional distress, fatigue and cognitive difficulties. Further research is needed to explore differences in subjective stress by age.