Small mpMRI index lesions are favorable marker for guiding active surveillance strategies

Small index lesions on initial multiparametric MRI (mpMRI) were linked to a less aggressive clinical course for patients with prostate cancer on active surveillance, showing they may be a favorable marker to guide the timing of subsequent imaging and personalize patient care.¹

The findings were presented by Jayant Siva, National Institutes of Health, in a poster at the 2023 Society of Urologic Oncology (SUO) Annual Meeting.

“Our study showed that patients who had small index lesions on their initial MRI—so lesions that are less than 7 mm—had favorable outcomes, indicating that their cancers grew a lot less and their progression was a lot lower than normal. So, it basically indicated that this smaller lesion size on initial MRI is a favorable marker to guide physicians, because it likely means that the patient does not need to have repeat biopsies every 2 years; the biopsy interval can be longer,” said Jayant Siva.

Explaining the study background, Siva et al wrote on their poster, “Little is known about the natural history of patients with low-risk disease who have small index lesions (<7 mm) on [initial] prostate MRI and are currently on active surveillance.”

Accordingly, the investigators queried a National Cancer Institute prospective database of patients who had small index lesions(<7 mm) and were on active surveillance between 2007 and 2022. Patients were included if, following MRI, they had benign disease or Gleason Grade Group 1 (GG1) disease.

Overall there were 115 patients who met the inclusion criteria. The average follow-up for these patients was 4.3 years.

There were 88 evaluable patients with lesions ≤7 mm on initial MRI, 36 with benign disease and 52 with GG1. The index lesion size on initial mpMRI was 5.20 +/- 2.03 mm (range, 0 - 7.0) and the index lesion size on their most recent mpMRI was 0.45 +/- 2.80 mm (range, -2.78 – 23.08; P = .242). Index lesion PI-RADS scores were 2 (n = 22), 3 (n = 31), and 4 (n = 35).

There were 36 evaluable patients with lesions ≤5 mm on initial MRI, 17 with benign disease and 19 with GG1. The index lesion size on initial mpMRI was 3.31 +/- 1.90 mm (range, 0 - 5.0) and the index lesion size on their most recent mpMRI was 0.97 +/- 4.01 mm (range, -1.70 – 23.08; P = .097). Index lesion PI-RADS scores were 2 (n = 13), 3 (n = 14), and 4 (n = 9).

“Lesions both ≤5 mm and ≤7 mm demonstrated no statistically significant change in maximum diameter between first and last MRI. Few evaluable lesions shrank over time,” wrote Siva et al.

Overall, the mean time to disease progression to GG2 was 4.35 years, and the mean time to disease progression to GG3 disease was 4.69 years. The rate of disease progression to radical therapy was 15.79% (n = 18). The average time to progression to radical therapy was 5.51 years following initial biopsy.

Of note, within the first 2 years following initial MRI, there were only 6 patients (5.2%) who had disease progression to GG3 and only 3 patients (2.6%) who had disease progression necessitating radical therapy.

Another way to look at it, according to the authors, is that for these patients with small index lesions, if repeat biopsy had been conducted at 2 years, 97% would be able to remain on active surveillance.

Among patients who had no index lesion on initial MRI, 0% had disease progression to GG3 or radical therapy.

In an interview with Urology Times at the SUO meeting, Siva reiterated the study’s findings that small index lesions are a favorable indicator that a patient on active surveillance has a less aggressive prostate cancer.

“Our study showed that patients who had small index lesions on their initial MRI—so lesions that are less than 7 mm—had favorable outcomes, indicating that their cancers grew a lot less and their progression was a lot lower than normal. So, it basically indicated that this smaller lesion size on initial MRI is a favorable marker to guide physicians, because it likely means that the patient does not need to have repeat biopsies every 2 years; the biopsy interval can be longer.”

Reference

1. Siva J, Pillai A, Mendhiratta N, et al. Clinical outcomes of patients on active surveillance for low-risk prostate cancer with small index lesions on MRI. Presented at: 2023 Society of Urologic Oncology Annual Meeting. November 28 – December 1, 2023; Washington, DC. Abstract 34.