Postneoadjuvant Whipple Resections Show Significant Residual Microscopic Tumor Beyond Grossly Identified Tumor Bed: Implications for Accurate Tumor Staging.

Abstract

Neoadjuvant chemotherapy plays a vital role in the treatment of pancreatic ductal adenocarcinoma (PDAC), but treatment effect complicates pathologic examination of postneoadjuvant Whipple resections. Institutional practice is variable but current Pancreatobiliary Pathology Society (PBPS) guidelines suggest extensive microscopic examination of the tumor bed (TB). In practice, gross identification of TB is challenging and may lead to an inaccurate assessment of tumor size. The purpose of this study is to evaluate the adequacy of current practice in postneoadjuvant Whipple resections for pathologic staging. A single institutional prospective cohort was assessed, including 29 entirely submitted (ES) specimens and 10 current PBPS guideline-based (CG) specimens. Cases were evaluated for TB gross measurement, TB microscopic tumor, nontumor bed (N-TB) microscopic tumor, overall size assessment by microscopic evaluation, and presence of lymph nodes with metastases. ES and CG specimens showed similar overall residual tumor size measurements under the current PBPS guidelines protocol, but with the entire submission, tumor size increased by an average of 0.5 cm (range: 0.0 to 2.1 cm). Twenty-eight percent had an upstaged ypT due to a significant N-TB tumor. These findings delineate the limitations of gross TB assessment in postneoadjuvant Whipple resections for adequate pathologic staging and appropriate prognostication.