BRONX, NY — Assessing tumor growth and regression to determine a treatment’s efficacy over time can be challenging on an individual basis. In a real-world setting, variability between practitioners can make comparisons between therapies in a large population very difficult.

A study presented Saturday at the 2018 American Society of Clinical Oncology Annual Meeting in Chicago indicates that researchers at the James J. Peters VAMC in the Bronx, NY, and colleagues have developed a reliable way to assess treatment efficacy and estimate overall survival outside of the clinical trial setting.1

The first application provided new insight into the use of abiraterone and enzalutamide for metastatic prostate cancer.

The researchers analyzed data from more than 10,000 patients in the VA Informatics and Computing Infrastructure (VINCI), using a novel set of equations that could simultaneously calculate exponential growth and regression rates in tumors during cancer treatment. In previous research, the team had demonstrated that the exponential tumor growth rate (g) enables calculation of doubling time and also corresponds with overall survival.

The study validated use of the equations in 5,890 veterans with metastatic prostate cancer who received chemotherapy with either abiraterone or enzalutamide or both. Researchers assessed the impact of demographic factors and treatment on outcomes based on VINCI data. Patients had a median age of 75, with 2,596 age 80 or older. The cohort included 597 (23%) African American men, and 88% of patients had multiple PSA values recorded. The team had sufficient information to calculate growth and regression rates in about 84% of veterans.

Patients receiving abiraterone and enzalutamide had nearly identical tumor growth rates in the first-line setting, indicating that the two drugs had comparable efficacy. In the second-line, patients receiving enzalutamide had a lower growth rate. The researchers noted, however, that their analysis found that the majority of patients who received first-line abiraterone had constant, and superior, growth rates which suggested that staying on abiraterone rather than switching may be more beneficial for those patients.

The researchers determined that tumor growth rate was independent of age and location of treatment. It was also independent of race, indicating that the drugs provided equivalent benefit to African American and non-African American veterans, an important finding given the frequently more aggressive course of prostate cancer in African American men.
The researchers concluded that exponential tumor growth rate provided an “excellent measure of efficacy” that highlights its value in future outcomes research.

1Leuva H, Sigel K, Wilkerson J, et al. A novel approach to mine the Veterans Administration Informatics and Computing Infrastructure (VINCI) allows one to assess the efficacy of cancer therapies: Abiraterone and enzalutamide in Veterans with metastatic prostate cancer. J Clin Oncol 36, 2018 (suppl; abstr 6586)