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DIFFERENCES IN RESPONSE OF MESORECTAL AND LATERAL LYMPH NODES AFTER NEOADJUVANT CHEMORADIOTHERAPY FOR RECTAL CANCER: EVIDENCE FROM RADIOLOGY AND PATHOLOGY
Zixuan Zhuang
*, Yang Zhang, Xuyang Yang, Xiangbing Deng, Ziqiang Wang
West China Hospital of Sichuan University, Chengdu, Sichuan, China
AimThe differential regression patterns of lateral pelvic lymph nodes (LLN) and mesorectal lymph nodes (MLN) after neoadjuvant chemoradiotherapy (NCRT) in rectal cancer remain poorly understood. This study investigates the imaging regression patterns of MLN and LLN, evaluates differences in pathological lymph node regression grade (LRG), and assesses the prognostic impact in locally advanced rectal cancer (LARC) patients undergoing radical resection and LLN dissection (LLND) after NCRT.
Methods110 LARC patients undergoing radical resection and LLND after NCRT between 2016 and 2024 were enrolled. All visible MLN and LLN on initial MRI were matched node-by-node on post-NCRT MRI, measured the short axis (SA), and calculated the regression of lymph nodes (LN). Pathological LRG scores were based on the proportion of tumor cells and fibrosis, with the maximum LRG (LRG-max), the sum score of LRG (LRG-sum) of each LN for an individual patient and LRG-ratio (LRG-sum divided by the number of positive LN) were calculated. Differences and correlations between MLN and LLN in radiological and pathological regression were analyzed at both LN and patient levels. Cox regression was employed to explore the relationship between LRG-sum and prognosis.
ResultsA total of 1744 lymph nodes were assessed via MRI, including 811 MLN and 933 LLN on initial scans, and 546 MLN and 969 LLN on post-NCRT scans. MLN demonstrated a significantly higher disappearance rate (32.7% vs. 2.4%, P < 0.0001) and greater SA regression (0.596±0.333 vs. 0.214±0.242, P < 0.0001) compared to LLN. 2108 lymph nodes were re-evaluated for the presence of fibrosis or residual cancer cells, including 916 MLN and 1192 LLN. Subgroup analysis of 25 patients with both MLN and LLN metastases showed higher LRG-max (mean rank) (37.13 vs. 21.37, P = 0.011) and LRG-ratio (3.45±1.29 vs. 2.47±0.96, P = 0.0003) in LLN than MLN. After a median follow-up of 36 months (IQR 8–96 months), 28 patients (25.5%) died, and 45 (40.9%) experienced tumor recurrence or metastasis. Patients were categorized according to the cutoff points of LRG-sum distribution: LRG low (LRG-sum 0 to 1), LRG middle (LRG-sum 2 to 4), and LRG high (LRG-sum ?5). The 3-year DFS rates for low, middle, and high MLN LRG-sum groups as 70.9%, 58.2%, and 22%, respectively (P < 0.001). Corresponding rates for LLN were 78.2%, 44.8%, and 29% (P < 0.001).
ConclusionLLN exhibited significantly lower imaging regression and disappearance rates, higher pathological residual cancer presence, poorer treatment response, and worse prognosis with elevated cumulative LRG scores compared to MLN following NCRT, indicating that LLN was more tolerant to NCRT.
A study workflow
Study sample radiological and pathological characteristics
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