| 1. Uncertainty regarding the definition of the “discontinuity” in peritumoral TD diagnosis |
There is no international consensus as to the definition of the distance from the advancing edge of the main body of the primary tumor or bowel wall for peritumoral TD. Some criteria have been proposed such as 1) ≥5 mm,
11
,
26
2) ≥1 cm,
23
and 3) no clear connection.
27
The “5‐mm” is the only criterion for peritumoral TD that had been predetermined in a multicenter study,
11
,
26
and this criterion has been used across Japan since 2013.
19
|
| 2. Uncertainty regarding the appropriateness of isolated intravascular or perineural TDs not being taken into account in tumor staging |
Intravascular or perineural TDs have been included in many studies to analyze the prognostic impact of TDs and there is no evidence that the prognostic value of tumor staging is improved by excluding such lesions from staging factors. The prognostic power of the T stage was improved by treating isolated intravascular/perineural deposits as a pT3‐determining factor in tumors otherwise diagnosed as pT1 or pT2.
14
,
15
|
| 3. Lack of meaningful rationale of distinguishing TDs with identifiable vascular or neural structures from other TDs in tumor staging |
None of the studies that investigated the prognostic value of TDs have excluded TDs with identifiable vascular or neural structure from the analyses and there is no evidence that the prognostic value of tumor staging is improved by excluding such TDs from staging factors. Nodular TD accompanied by the finding of venous/perineural invasion in the nodule has a prognostic value that is greater than other types of TDs.
11
,
15
Impaired diagnostic reproducibility of tumor staging is inevitable due to interobserver disagreement regarding the judgment for vascular or neural structure in the lesion. Kappa statistic was reportedly 0.61 between nodular TD with venous/perineural invasion and other types of extramural discontinuous lesion.
11
|
| 4. Lack of evidence for the value of the N1c category |
A multicenter study showed that TNM7 adopting the N1c category is superior to TNM6 characterized by the contour rule, but not to TNM5 characterized by the size rule in terms of its prognostic power.
26
Under the N1c rule, the tumor stage does not change according to the number of existing TDs in the resected specimens, but the number of TD has prognostic information.
10
,
11
,
36
,
37
Impaired diagnostic reproducibility of tumor staging is inevitable due to interobserver disagreement on the distinction between TDs and LNM. Kappa statistic was 0.74 between LNM and TDs,
14
and 0.38 between “nodal” or “non‐nodal” origin.
18
An increasing number of studies indicate the value of a modified staging system in which TDs are counted individually same as lymph nodes in the final pN determination ( see Table 3).
|
