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Magnetic resonance imaging (MRI) directed surgical decision making for lateral pelvic lymph node dissection (LPLND) in rectal cancer after total neoadjuvant therapy (TNT).
Oliver Peacock1, Naveen Manisundaram1, Youngwan Kim1, Nir Stanietzky2, Emma B. Holliday3, Arvind Dasari4, Melissa Taggart5, Harmeet Kaur2, Brian Bednarski1, Tsuyoshi Konishi1, George J. Chang1
1Colorectal Surgical Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States, 2Radiology, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States, 3Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States, 4Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States, 5Pathology, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States

Objective: LPLN metastases are an important cause of preventable local failure in rectal cancer. Advances in pre-operative evaluation with high-resolution rectal MRI have improved the detection of LPLN metastasis, but the optimal surgical treatment strategy for patients with LPLN including for dissection is evolving. The aim of this study was to evaluate clinical and oncological outcomes following image directed surgical decision making for LPLND in patients at a single comprehensive cancer center.

Methods:
A retrospective consecutive cohort analysis was performed of rectal cancer patients with enlarged LPLN on pre-treatment MRI between January 2016 and May 2021. Data were obtained from a prospective database and augmented with natural language processing and direct record review. All patient-level data were aggregated and analyzed using the Palantir Foundry platform (https://www.palantir.com/palantir-foundry/). Patients were categorized as LPLND or not dissected. The main outcomes were short-term perioperative and oncological outcomes. Morbidity was classified by Clavien-Dindo grade.

Results:
A total of 155 patients with enlarged LPLN on pre-treatment imaging were identified. All patients received TNT. The median follow up was 23 months (IQR 12-40). After multidisciplinary review of post-treatment imaging according to MRI response criteria, 86 patients (55.5%) underwent LPLND. Mean age was 53 (SD+/- 12) years, and 54 (34.8%) were female. Median BMI was 29.0 (IQR 26.0-35.0) in the LPLND and 28.3 (IQR 25.2-32.4) in non-LPLND groups. Median tumor distance from the anal verge was 6 cm (IQR 4-7) and did not differ between groups . Rates of sphincter preservation (p=0.139) and median blood loss did not differ (p=0.770). Median pre- and post-treatment short axis lymph node size was 11 mm (IQR 8-17) and 6.5 mm (IQR 5-10) for the LPLND group, compared with 7 mm (IQR 5-10) and 3 mm (IQR 0-5) in the non-LPLND group (p<0.0001). Total operative time (510 vs 426 minutes; p=0.001) was greater in the LPLND group. There was no difference in median length of stay (5 vs 5 days) or major morbidity (16.3% vs. 15.9%). There was no difference in the sexual dysfunction rate (3.0% vs 7.0%), but there was a difference in rate of urinary retention (25.6% vs. 4.4%; p<0.0001). Pathologically positive LPLNs were identified in 32.6%. The lateral local recurrence (4.7% vs. 4.3%) or distal failure (14.0% vs 20.3%) rates did not differ between the LPLND and non-LPLND groups.

Conclusion:
LPLN were persistently positive in one-third of at-risk rectal cancer patients following TNT. Lateral pelvic recurrences in these patients can be avoided with appropriate MRI directed selection of patients for LPLND without increase in major morbidity.


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