Does Extramural Vascular Invasion Predict Response to Neoadjuvant Therapy in Locally Advanced Rectal Cancer?

Introduction: Extramural vascular invasion (EMVI) is associated with distant recurrence after treatment of locogionally advanced rectal adenocarcinomas (LARCs), but its use as a marker for response to neoadjuvant therapy is less well understood. We examined the relationship between EMVI and tumor or nodal category downstaging after treatment of LARCs with neoadjuvant therapy.

Methods: Patients with EMVI categorized on initial staging pelvic MRI for LARC who underwent curative-intent surgery after neoadjuvant therapy at MD Anderson Cancer Center from 2016 to 2022 were identified. Patients received either preoperative chemoradiation or total neoadjuvant therapy (TNT). Associations between EMVI and demographic, radiologic, and clinicopathologic variables were analyzed.

Results: EMVI was associated with higher rates of lymphovascular invasion (LVI) (46.2% vs. 27.8%, P = .001) and perineural invasion (PNI) (51.9% vs. 28.4%, P < .001) on final pathology. Patients with EMVI were more likely to have cT4 tumors (31.7% vs. 16.3%, P = .004) and cN+ status (86.8% vs. 66.3%, P = .001) and more likely to be treated with TNT rather than chemoradiation alone (62.3% vs. 41.9%, P = .005). EMVI was associated with a lower rate of pathologic complete or near-complete response (20.1% vs. 34.2%, P = .018), downstaging to ypT0-2 from cT3/4 tumors (14.9% vs. 44.4%, P = .0001), and downstaging to ypN0 from cN+ status (47.9% vs. 66.4%, P = .015).

Conclusions: Rectal tumors with EMVI are more likely to have higher clinical stage, less likely to respond to neoadjuvant therapy despite increased use of TNT, and more likely to have high-risk features for recurrence. This suggests EMVI is a marker of disease with poorer response to neoadjuvant therapy. Disease biology should be strongly considered in treatment decision-making, and new treatment strategies are needed to improve disease response.