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