This study aimed to evaluate the prognostic significance of tumor regression rate according to radiation phase and histologic subtype in patients with locally advanced cervical cancer (LACC) treated with chemoradiation. We retrospectively reviewed the medical records of 398 patients with FIGO stage IIB-IVA cervical cancer treated with concurrent chemoradiotherapy (CCRT) between 2001 and 2019. Tumor response was assessed using serial magnetic resonance imaging (MRI) at three time points: pre-treatment, post-external beam radiotherapy (EBRT), and post-intracavitary radiotherapy (ICR). Tumor regression pattern according to histologic subtype and radiation phase (EBRT and ICR) was evaluated. Overall survival (OS) and progression-free survival (PFS) were the primary outcomes. Of 398 patients, 44 patients had adenocarcinoma/adenosquamous carcinoma (AC/ASC) and 354 patients had squamous cell carcinoma (SCC). AC/ASC was associated with significantly worse PFS and OS than SCC (p < 0.001). AC/ASC had a relatively poorer regression rate in response to EBRT than SCC (p < 0.001), whereas there was no significant difference in overall tumor regression rate after completion of RT (EBRT and ICR) between the two histologic subtypes. Multivariable analysis demonstrated AC/ASC histology to be an independent prognostic factor of decreased PFS and OS. Moreover, tumor regression rate after completion of EBRT (post-EBRT tumor regression rate (EBRT_regression ≤ 26%) and proportion of tumor regression during EBRT to overall tumor regression (EBRT_proportion ≤ 40%) were independent predictors of poor survival in patients with LACC. Tumor regression pattern of LACC in response to CCRT differs according to histologic subtype. AC/ASC histology and poor tumor response to EBRT are independent prognostic factors for worse survival in patients with LACC. Further studies are needed to develop a CCRT protocol that is specialized for patients with AC/ASC.

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