pT4a inasive colorectal adenocarcinoma

Determination of T4a (tumor penetrates to the surface of the visceral peritoneum) and T4b (tumor directly invades or is adherent to other organs or structures) can sometimes be problematic:
 First, serosal surface (visceral peritoneum) involvement can be missed if the specimen is not adequately sampled for histologic examination.
 Second, the serosal surface may be confused with the circumferential margin (radial margin) or mesenteric margin, which is a nonperitonealized surface created surgically by blunt or sharp dissection. A T3 tumor may involve the radial margin and a T4 tumor may have a negative radial margin.
 Third, a surgically induced perforation at the tumor site may be confused with true tumor perforation, which requires clarification from surgeons.
 Fourth, adherence of other organs or structures at the tumor site does not necessarily qualify for T4b. Histologically, the adherent site may show only inflammatory changes, abscess formation and/or fibrosis, but without direct tumor involvement.
 Finally, there is some confusion about the definition of visceral peritoneum involvement.

Clearly, the interpretation of T4a can be unequivocal if,

• (I) tumor cells are present at the serosal surface with inflammatory reaction, mesothelial hyperplasia, and/or erosion;
• or (II) free tumor cells are seen on the serosal surface with underlying ulceration of the visceral peritoneum.

Tumor cells close to, but not at, the serosal surface, with mesothelial inflammatory and hyperplastic reactions, which may be considered T4a by some investigators.

However, identification of tumor cells close to, but not at, the serosal surface would be considered T4a by some investigators if there are associated mesothelial inflammatory and/or hyperplastic reactions.

Apparently, the application of this third criterion is prone to subjective judgment and lacks reproducibility.

It is noted that in the updated cancer protocols and checklists by College of American Pathologists (CAP), only the first two criteria are listed as the diagnostic features of T4a, and the third criterion is deleted.

References

 http://www.thejgo.org/article/view/410/821