Abstract
The introduction of TNM 8 into UK pathology practice in January 2018 considers tumour deposits in colorectal cancer staging for the first time. The impact of this new classification on pathology reporting practices has yet to be evaluated. A clinical audit was conducted, comparing consecutive colorectal cancer resection specimens reported under TNM 5 classification guidelines in 2017 (n=177) and TNM 8 guidelines in 2018 (n=234). Tumour features (venous invasion, perineural invasion, lymph node metastatic disease, tumour deposits) and changes in reporting practices were evaluated among four specialist gastrointestinal pathologists working within a large pathology department. Adoption of TNM 8 practice led to an approximate doubling in the use of ancillary stains (41.0% of TNM 8 versus 22.0% of TNM 5 cases, P<0.001) to help evaluate tumours. A narrowing of the range between pathologists was observed in reporting cases as having one or more form of regional, extramural, discontinuous tumour (TNM 5 range=50.0-79.0%, TNM 8 range=57.8-65.7%), with no change in the overall proportion of cases reported as such (62.7% versus 62.4%, P=0.95). However, significant interobserver variation in reporting rates for individual parameters remained. TNM 8 colorectal cancer staging offers potentially greater reproducibility in pathology reporting of regional, extramural, discontinuous disease with similar proportions of patients reported as having one or more of these forms of tumour spread compared with TNM 5. Further guidance in defining individual features is required to reduce interobserver variation in pathology assessments and to help elucidate the clinical significance of each parameter.
Highlights
The introduction of TNM 8 into UK pathology practice in January 2018 considers tumour deposits in colorectal cancer staging for the first time
Tumour features and changes in reporting practices were evaluated amongst four specialist gastrointestinal pathologists working within a large pathology department
The proportion of cases reported by the four pathologists participating in the audit ranged from 17-35%, demonstrating that each contributed a reasonable caseload in both TNM 5 and TNM 8 cohorts, with some variation in the proportion of cases reported by individual pathologists upon transfer from TNM 5 to TNM 8 rules
Summary
The introduction of TNM 8 into UK pathology practice in January 2018 considers tumour deposits in colorectal cancer staging for the first time. Foci of tumour discontinuous from the primary tumour but within pericolic or perirectal fat, called tumour deposits (TD), have been defined and classified variably within different editions of the Union for International Cancer Control (UICC) TNM classification This directly impacts the handling and interpretation of CRC cases by pathologists and, in turn, cancer staging and potentially patient care. The sixth edition of UICC TNM (TNM 6), published in 2002, discounted size but classified discontinuous tumour nodules on the basis of contour, with smooth rounded nodules considered nodal metastases and nodules with irregular contours considered likely to represent extramural venous invasion (EMVI), the latter classified under the V1 (microscopic venous invasion) or V2 (macroscopic venous invasion) coding systems.[2] The seventh edition of UICC TNM (TNM 7), published in 2009, formally introduced the term “tumour deposits”, defined as discrete macroscopic or microscopic nodules of cancer in the pericolorectal adipose tissue’s lymph drainage area of a primary carcinoma that are discontinuous from the primary and without histological evidence of residual lymph node.[3] TDs were considered to represent discontinuous spread, venous invasion or totally replaced lymph nodes. Given concerns over a lack of evidence base for introducing these changes and over reproducibility, some countries, including the United Kingdom, did not adopt TNM 6 or TNM 7 and continued to apply TNM 5 staging for CRC.[4,5,6]
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