# Response Prediction of Chemoradiotherapy for Rectal Cancer Using Rapid Semi-Automated Flow Cytometry

## TL;DR

This study explores using flow cytometry to predict how well rectal cancer patients will respond to chemoradiotherapy treatment.

## Contribution

The study introduces rapid semi-automated flow cytometry as a potential biomarker for predicting CRT effectiveness in rectal cancer.

## Key findings

- A higher proportion of cells in the Over G2/M phase correlates with greater tumor shrinkage after CRT.
- PET scans showing FDG uptake disappearance also correlate with higher Over G2/M cell proportions.
- Celltac PEAK flow cytometry analysis was used to measure cell cycle phases in rectal cancer biopsies.

## Abstract

There is no reliable biomarker for predicting the effectiveness of CRT in rectal cancer. The aim of our study is to assess the potential value of cell cycle analysis by rapid semi-automated flow cytometry to predict the effectiveness of CRT. Thirty-two patients with rectal cancer who underwent CRT were enrolled in this study. The cell cycles of biopsy specimens from rectal cancer before CRT are analyzed using Celltac PEAK as flow cytometer. The group with a reduction rate of 30% or more in CT has a significantly higher proportion of cells in the Over G2/M phase. The group with PET accumulation disappearance on 18F-FDG PET/CT has significantly higher proportion of Over G2/M as well. A high proportion of cells in the Over G2/M phase could be a potential biomarker for tumor shrinkage effects in CRT for rectal cancer.

(1) Background: The effectiveness of chemoradiotherapy (CRT) for rectal cancer varies greatly among patients, and no reliable biomarker for predicting treatment response currently exists. We investigated whether cell cycle analysis using rapid semi-automated flow cytometry could predict the effectiveness of CRT. (2) Methods: This prospective study included 32 patients with rectal cancer undergoing CRT. The cell cycle of biopsy specimens from rectal cancer patients before CRT was semi-automatically and rapidly analyzed using Celltac PEAK as flow cytometer. The proportion of cell cycle phases is compared with treatment response after CRT. (3) Results: Patients with a tumor reduction rate ≥ 30% on CT showed a significantly higher proportion of cells in the Over G2/M phase compared with those with <30% reduction (median 2.45% vs. 0.95%, p = 0.022). Similarly, tumors demonstrating disappearance of FDG uptake after CRT had a significantly higher proportion of cells in the Over G2/M phase compared with those with persistent FDG uptake (median 4.05% vs. 1.24%, p = 0.024). (4) Conclusions: A high proportion of cells in the Over G2/M phase could be a potential biomarker for predicting tumor shrinkage in CRT for rectal cancer.