Genomic Complexity Predicts Resistance to Endocrine Therapy and CDK4/6 Inhibition in Hormone Receptor-Positive (HR+)/HER2-Negative Metastatic Breast Cancer

PURPOSE

Clinical biomarkers to identify patients unlikely to benefit from CDK4/6 inhibition (CDK4/6i) in combination with endocrine therapy (ET) are lacking. We implemented a comprehensive circulating tumor DNA (ctDNA) analysis to identify genomic features for predicting and monitoring treatment resistance.

EXPERIMENTAL DESIGN

ctDNA was isolated from 216 plasma samples collected from 51 patients with hormone receptor-positive (HR+)/HER2-negative (HER2-) metastatic breast cancer (MBC) on a phase II trial of palbociclib combined with letrozole or fulvestrant (NCT03007979). Boosted whole-exome sequencing (WES) was performed at baseline and clinical progression to evaluate genomic alterations, mutational signatures, and blood tumor mutational burden (bTMB). Low-pass whole-genome sequencing was performed at baseline and serial timepoints to assess blood copy-number burden (bCNB).

RESULTS

High bTMB and bCNB were associated with lack of clinical benefit and significantly shorter progression-free survival (PFS) compared with patients with low bTMB or low bCNB (all P < 0.05). Dominant APOBEC signatures were detected at baseline exclusively in cases with high bTMB (5/13, 38.5%) versus low bTMB (0/37, 0%; P = 0.0006). Alterations in ESR1 were enriched in samples with high bTMB (P = 0.0005). There was a high correlation between bTMB determined by WES and bTMB determined using a 600-gene panel (R = 0.98). During serial monitoring, an increase in bCNB score preceded radiographic progression in 12 of 18 (66.7%) patients.

CONCLUSIONS

Genomic complexity detected by noninvasive profiling of bTMB and bCNB predicted poor outcomes in patients treated with ET and CDK4/6i and identified early disease progression before imaging. Novel treatment strategies including immunotherapy-based combinations should be investigated in this population.

Doxorubicin and dose-escalated cyclophosphamide with granulocyte colony-stimulating factor for the treatment of hormone-resistant prostate cancer

PURPOSE

The goals of this study were to define the efficacy and toxicity of doxorubicin and dose-escalated cyclophosphamide (Cy) along with granulocyte colony-stimulating factor (G-CSF) in the treatment of hormone-refractory prostate cancer (HRPC), to determine the maximal-tolerated dose (MTD) of Cy in this regimen, and to evaluate the impact of prior pelvic irradiation (XRT) on MTD and toxicity.

PATIENTS AND METHODS

Thirty-five patients were treated every 21 days with fixed-dose doxorubicin (40 mg/m2) and Cy 800 to 2,000 mg/m2 (in a cohort dose-escalation schema) along with G-CSF.

RESULTS

Five of 15 patients (33%) with measurable disease obtained an objective response. Sixteen of 35 patients (46%) had a greater than 50% decrease in prostate-specific antigen (PSA) level (95% confidence interval [CI], 28.8% to 63.4%). Ten of 35 patients (28.6%) had a greater than 75% decrease in PSA level. The median survival time was 11 months. The median survival duration of patients with a greater than 50% decrease in PSA level was 23 months, versus a median survival time of 7 months in patients without a PSA response (P = .02). Although 33% of cycles were associated with grade 4 neutropenia, febrile neutropenia occurred in only 7.8% of all cycles. Thrombocytopenia and anemia were rare. Nonhematologic toxicity was minimal. Patients who had received prior pelvic XRT had a lower Cy MTD, but their hematologic toxicity was not appreciably different.

CONCLUSION

This is a well-tolerated, active regimen for the treatment of HRPC. Toxicity was not different in patients with prior pelvic XRT, although these patients had a lower MTD.

Radioimmunoassay for the detection of antigen-specific IgM, IgG, and IgA in equine sera

A radioimmunoassay was developed to discriminate immunoglobulin (Ig) classes specific for the J-5 mutant of Escherichia coli (serotype O:111-B4). Adult horses were periodically inoculated IM with a nonviable suspension of the J-5 mutant emulsified in Freund's incomplete adjuvant. Before and after the horses were inoculated, sera were collected sequentially and examined by radioimmunoassay. Rabbit anti-(horse) Ig and [125I]protein A served as the indicator system. Antigen-specific IgM, IgG, and IgA were observed to follow a classic immune response. The radioimmunoassay offers a valuable tool for the discrimination of circulating, antigen-specific Ig in the horse.