E1774. Mind the Gap: Differences Between Pathology and Radiology Staging of Hepatocellular Carcinomas - What Radiologists Need to Know?
  1. Guilherme Moura Cunha; University of California San Diego
  2. Mojgan Hosseini; University of California San Diego
  3. Andrew Boehringer; University of California San Diego
  4. Claude Sirlin; University of California San Diego
  5. Kathryn Fowler; University of California San Diego
Hepatocellular carcinoma (HCC) staging is mandatory to assess the burden of disease, inform management decisions and patient prognosis [1]. In the transplant setting the radiologic T stage determines candidacy [1, 2], whereas following transplantation the explant liver is assigned a pathological T stage [3]. While comparison of radiological and pathological T stage should be straightforward, the staging conventions are different (i.e. radiological T2 stage is not equivalent to pathological T2 stage) (Slide 1) [3, 4]. These differences challenge the ability to perform radiological-pathological correlation and potentially introduce discrepancy in prognostication.

Educational Goals / Teaching Points
This exhibit aims to: i) review pathology and radiology HCC T staging systems; ii) highlight the differences that may result in poor rad-path correlations, particularly in the transplant setting; iii) address the components of each staging system that are predictive of patient outcome; and, iv) explore the possibility of a single unified TNM system.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
How pathologists stage HCC: Slide 2 describes pathology T staging [3]. How radiologists stage HCC: Slide 3 illustrates the radiologic T staging [4]. How pathology staging and the radiologic T stage differ: Although both systems consider size and number of HCC, major differences are observed particularly within the intermediate stages, i.e. T2 stage (slides 4, 5). A direct comparison of the radiology T-stage to the pathology T-stage is not possible. Patient outcome: Studies have investigated prognostic features associated with T stage [5-7]. Gross vascular invasion outperforms size and number as an independent predictor of poor outcome, but microvascular invasion, i.e. tumor cells within an endothelium-lined space seen only under the microscope, is not an independent outcome predictor [8]. In patients with a single tumor without vascular invasion or microvascular invasion only, size has no effect on survival. The number of small foci of HCC seem also to not affect outcomes [6-9]. Imaging has a limited ability to detect microvascular invasion and gross small vessel invasion. Hence, size and number of HCCs compel the radiologic T staging. Although these are arguably the best available surrogate marker for entities that are difficult to detect on imaging before liver transplantation [9], different staging system used in the pre- and post-transplant settings hinders researchers’ ability to assess the accuracy of imaging and its relation to prognosis.

Radiologists should be aware of the major differences that exist between radiologic and pathology staging systems for HCC; A single unified staging system may facilitate the communication of results and improve management guidance based on outcome prediction.