Letter to the Editor: “Usefulness of texture features of apparent diffusion coefficient maps in predicting chemoradiotherapy response in muscle-invasive bladder cancer”

by Masamitsu Hatakenaka (mhatakenaka@sapmed.ac.jp)

Usefulness of texture features of apparent diffusion coefficient maps in predicting chemoradiotherapy response in muscle-invasive bladder cancer

Dear Editor in Chief,

I have read with a great interest the article entitled “Usefulness of texture features of apparent diffusion coefficient maps in predicting chemoradiotherapy response in muscle-invasive bladder cancer” by K. Kimura et al. [1]. The study results were clinically very important and reasonable. However, adding probable mechanisms to explain the results could deepen readers’ understanding and enhance motivation for further studies.

As mentioned in reference [2], mean ADC negatively correlates with Ki-67 labeling index, lower mean ADC indicating higher Ki-67 expression. Also in reference [3], bladder cancers with metastasis or recurrence show lower ADC compared to those without. These results indicate that bladder cancer with lower ADC has higher malignant potential and seems to conflict with the results that muscle-invasive bladder cancer with lower ADC predicts favorable chemoradiotherapy response. I published similar results in regards to head and neck cancer and proposed the probable mechanisms explaining this seemingly inconsistent results by applying bystander effect [4]. Briefly, cancer with lower ADC tends to show higher cellularity [5] and be prone to bystander effect of radiotherapy, being sensitive to radiotherapy. The prognosis would be determined by the balance between chemoradiatiotherapy sensitivity and malignant potential of its own when treated with chemoradiotherapy. As for radiosensitive cancer such as head neck squamous cell carcinoma, chemoradiatiotherapy sensitivity, negatively correlated with ADC, mainly affects prognosis, resulting in cancer with lower ADC showing higher sensitivity and favorable prognosis. In contrast, for radioresistant cancer, malignant potential that is also negatively correlated with ADC dominantly determines prognosis, resulting in cancer with lower ADC showing higher malignant potential and poor prognosis.

It is a great pleasure if the authors would explain their considerations regarding the mechanism behind the results.