EP178 - Whole-Mount Sections for Assessing Tumor Regression in Rectal Cancer Specimens from Patients Treated with Neoadjuvant Therapy: Implications for Salvage Surgery

Saturday, May 10, 2025

3:53 PM – 3:58 PM PT

Location: Monitor 10, Sails Pavilion, Upper Level

ePoster Presenter(s)

Christina I. Lee, MD

Research Scholar
Memorial Sloan Kettering
New York, New York, United States

All of the relevant financial relationships listed below have been mitigated.
This individual has no financial relationships with ineligible companies.

Senior Author(s)

Julio Garcia-Aguilar, MD, PhD (he/him/his)

Chief Attending
Memorial Sloan Kettering Cancer Center
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.

Author(s)

NU

Nil Urganci, MD

Research fellow
Memorial Sloan Kettering
New York, New York, United States

Disclosure information not submitted.
MK

Min Jung Kim, MD, PhD

Visiting Investigator
Memorial Sloan Kettering
New York, New York, United States

Disclosure information not submitted.
IW

Iris H. Wei, MD

Assistant Attending
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.
Maria Widmar, MD, MPH (she/her/hers)

Assistant Attending
Memorial Sloan Kettering Cancer Center
Weill Cornell Medical Center
New York, New York, United States

All of the relevant financial relationships listed below have been mitigated.
This individual has no financial relationships with ineligible companies.
Emmanouil Pappou, MD, PhD

Assistant Attending
Memorial Sloan Kettering Cancer Center
New York, New York, United States

All of the relevant financial relationships listed below have been mitigated.
This individual has no financial relationships with ineligible companies.
Georgios Karagkounis, MD

Assistant Attending
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.
Garrett M. M. Nash, MD, MPH

Vice Chair of Quality and Safety
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.
J. Joshua Smith, MD, PhD

Associate Attending
Memorial Sloan Kettering Cancer Center
MSKCC, Weill Cornell Medical College
New York, New York, United States

Disclosure information not submitted.
Philip B. B. Paty, MD

Attending Surgeon
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Disclosure information not submitted.
Martin R. Weiser, MD

Vice Chair for Faculty Affairs
Memorial Sloan Kettering Cancer Center
Cornell Medical College
New York, New York, United States

All of the relevant financial relationships listed below have been mitigated.
This individual has no financial relationships with ineligible companies.
JS

Jinru Shia, MD

Attending
Memorial Sloan Kettering
New york, New York, United States

Disclosure information not submitted.

All of the relevant financial relationships listed below have been mitigated.

Christina I. Lee, MD: This individual has no financial relationships with ineligible companies.

Maria Widmar, MD, MPH: This individual has no financial relationships with ineligible companies.

Emmanouil Pappou, MD, PhD: This individual has no financial relationships with ineligible companies.

Martin R. Weiser, MD: This individual has no financial relationships with ineligible companies.

Image or Table (Do Not add text here):

Purpose/Background: The response of rectal cancer to neoadjuvant therapy (NAT) is variable and often results in the scattered distribution of discontinuous niches of residual cancer cells surrounded by scar. Understanding the distribution of residual cancer cells in the bowel wall and the mesorectum after NAT is important for surgical planning. Conventional pathology processing of rectal cancer specimens assesses only sections of the bowel wall and individually dissected lymph nodes leaving large portions of the mesorectum unexplored. In this study, we examined the distribution of residual cancers cells in the entire mesorectum using whole-mount sections of locally advanced rectal cancer (LARC) patients treated with NAT.

Methods/Interventions: Whole-mount sections of total mesorectal excision (TME) specimens from LARC patients treated with NAT were used to map the distribution of residual cancer cells. Presence of residual cancer cells was categorized in 3 groups: primary tumor beyond the bowel wall (ypT3+), tumor in the mesorectum (lymph nodes, extramural vascular invasion [EMVI], and tumor deposits [TD]), and tumor beyond the bowel wall (ypT3+) and in the mesorectum (lymph nodes, EMVI, and TD). Patterns of tumor regression in the bowel wall were categorized as fragmented regression (discontinuous niches of residual cancer cells), proximal/distal intramural spread (tumor cells extending from bulk of tumor under normal mucosa ≥1 mm distally or proximally), or tumor without mucosal involvement (tumor cells in deeper layers underneath normal mucosa). Results were stratified by clinical staging based on pelvic MRI.

Results/Outcomes: Whole-mount specimens from 157 patients with clinical stage II (31, 20%) or stage III (126, 80%) rectal cancer with an incomplete pathologic response to TNT (129, 82%), chemotherapy (23, 15%) or chemoradiation (5, 3.2%) were examined. The median age at diagnosis was 53 and 62% were males. A total of 118 (75%) had low anterior resection and 38 (25%) had abdominoperineal excision of the rectum. The quality of the TME was graded as complete in 149 (95%) patients, near complete in 7 (4.5) and incomplete in 1 (0.6%). Six (3.8%) of the patients had ypTis tumors, 15 (9.6%) ypT1, 48 (31%) ypT2, 83 (53%) ypT3, 5 (3.2%) ypT4; 55 (35%) were ypN+, 38 (24%) had EMVI, and 8 (5.1%) had TD. The distribution of the residual cancer cells and the patterns of non-uniform tumor regression are presented in the table. Overall, more than two thirds of the patients had residual cancer cells beyond the bowel wall and more than 40% had one or more non-uniform tumor regression patterns.

Conclusion/Discussion: The proportion of stage II and III rectal cancer patients with cancer cells beyond the muscularis propria, in the mesorectum or both, after NAT is high. In addition, many patients had non-uniform regression of the tumor in the bowel wall. These data raise concern about the use of local excision as salvage surgery for LARC patients treated with NAT.