(PM P14) Lymph Node Metastasis in Mucinous Appendiceal Adenocarcinoma

Introduction: Mucinous appendiceal adenocarcinoma (MAC) is a rare entity with limited data to inform prognostication and treatment. Lymph node metastasis (LNM) is a recognized prognostic factor in appendiceal cancers, but predictors and outcomes for LNM in patients with mucinous histology remain poorly defined.

Methods: Patients were identified from the 2004-2015 ACS NCDB® who underwent a segmental or partial colectomy as initial therapy for AJCC 8th Edition Stage I-IV MAC. Multivariable regression modeling established predictors of LMN. Classification tree analysis determined the predicted probability of LNM. Cox proportional hazards regression described 3-year survival (3YS).

Results: Of 3,168 patients, predictive factors of LNM (N=716, 22.6%) by multivariable regression analysis included increasing T stage (T4: odds ratio [OR] 6.18, p<0.0001), higher grade (moderately differentiated: OR 2.69, p<0.0001; poorly differentiated: OR 6.06, p<0.0001), and lymphovascular invasion (LVI) (OR 7.06, p<0.0001). On comparative regression, tumors with LVI had an increased rate of LNM (64.3%) compared to those with absent or unknown LVI (18.9%). Among those with absent or unknown LVI, grade further stratified LNM risk; LMN risk was 41.9% in poor or undifferentiated disease compared to 15.8% for well to moderately differentiated disease. LMN patients had significantly worse 3YS compared to those without LMN (hazard ratio 4.25, p<0.0001).

Conclusion: Predictors of LNM in MAC include T group, LVI, and grade. Even among low-risk patients, there is an appreciable risk of LNM associated with worse survival. This data can guide clinicians in their decision to pursue colectomy for MAC, particularly during synchronous cytoreductive surgery for carcinomatosis.