Pattern of retroperitoneal dissemination of primary peritoneum cancer: Basis for rational use of lymphadenectomy

Introduction: The rationale for lymphadenectomy in primary peritoneal cancer (PPC) is unclear. We sought to define the pattern of lymphatic metastasis in PPC and propose evidence-based rationale for lymphadenectomy in relevant cases. Methods: Patients with PPC undergoing primary surgery at Mayo Clinic were identified. Demographics, tumor characteristics, procedures performed and follow up were analyzed. Results: Forty eight patients with PPC were identified; 39 had stage IIIC (81.2%) and 9 (18.8%) had stage IV. Residual disease (RD) after primary surgery was microscopic in 6 cases (12.5%), less than 1 cm in 33 (68.8%), more than 1 cm in 9 patient (18.7%) with median survivals of 5.8, 3.2 and 1.3 years, respectively. Overall, 24 patients had lymphadenectomy performed (pelvic (PND) or paraortic (PAND) or both). Pelvic nodes were involved in 12/23 (52.7%) cases, while para-aortic nodes were involved in 5/21 (23.8%) of cases. The rate of simultaneously positive pelvic and para-aortic nodes was 20% (4/20). Nodal involvement was a poor prognostic factor with 5 year overall survival 63% vs. 25% (p = 0.014) in node positive vs. negative cases. Compared to patients with primary ovarian cancer (OC), OC cases had a higher rate of positive para-aortic nodes (57.6%: 77/132; p = 0.004). Conclusions: Retroperitoneal lymph nodes are a common site of metastases in PPC, therefore it is logically consistent to perform PND and PAND if a patient can be cytoreduced to microscopic RD in other sites or remove grossly positive nodes in patients with RD < 1 cm.