Growth rates of renal cell carcinoma (RCC) tumors differ by histologic subtypes, according to a new study.

Antonio Finelli, MD, of Princess Margaret Cancer Centre and the University Health Network, University of Toronto, and his colleagues analyzed 136 biopsy-proven RCC tumors in 134 patients managed with active surveillance (AS). Their objective was to compare growth rates and progression of different histologic subtypes of small RCC tumors. The investigators defined tumor progression as a sustained size of 4 cm or greater or volume doubling in 1 year. Patients underwent serial imaging with computed tomography, magnetic resonance imaging, or ultrasonography at 3, 6, and 12 months and annually thereafter.

At the time of their first tumor image, patients had a median age of 70 years and a median tumor diameter of 2.3 cm.

The median follow-up time for patients who remained on AS was 5.8 years. Clear cell RCC grew faster than papillary type 1 (0.25 vs 0.02 cm/yr on average), Dr Finelli’s team reported in European Urology. Overall, 60 lesions progressed: 49 (82%) by rapid growth (volume doubling), 7 (12%) increased to 4 cm or more, and 4 (6.7%) by both criteria. Metastases developed in 6 patients, all of whom had clear cell RCC.


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The predicted growth rates by diameter and volume for clear cell RCC over 3 years were 0.28 cm/yr and 2.4 cm3/yr, respectively. Over the same period, the average diameter- and volume-predicted growth rates of papillary type 1 tumors remained essentially unchanged (0.017 cm/yr and –0.006 cm3/yr).

In the absence of validated prognostic markers in patients with small renal masses managed by AS, the authors explained, better understanding of biopsy-characterized RCC tumor kinetics may enable improved individualized treatment recommendations.

Study limitations included the use of different imaging modalities and lack of central imaging review, the investigators noted.

Reference

Finelli A, Cheung DC, Al-Matar A, et al. Small renal mass surveillance: Histology-specific growth rates in a biopsy-characterized cohort. Eur Urol. Published online July 14, 2020. doi:10.1016/j.eururo.2020.06.053