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pT4a colorectal adenocarcinoma

Friday 15 February 2013

T4a colon adenocarcinoma; pT4a invasive colorectal adenocarcinoma

Cancer involvement of the colonic serosa is designated pT4a by the American Joint Committee on Cancer Staging Manual, 7th edition.

The manual defines criteria for pT4a as either tumor penetration of the serosa or comingling of cancer cells and mesothelial cells in histologic sections.

Unfortunately, the pT4a grouping is inconsistently applied, because these guidelines are overly limited: fibroinflammatory changes near the serosa may be associated with peritoneal metastases even in the absence of overt peritoneal penetration.

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.


Reliable ancillary techniques for detecting serosal penetration by the tumor and accurate criteria for stage assessment are needed.

Authiors evaluated the utility of cytologic preparations in determining tumor stage by comparing results of serosal scrape cytology with histologic stage assessment of 120 colon cancer resection specimens.

They correlated their findings with the presence and type of inflammatory changes near the serosa to determine which, if any, are reliable indicators of peritoneal penetration.

Cytologic smears from all pT1 and pT2 tumors were negative for carcinoma. 19% of pT3 tumors showed cancer in cytologic smears, all of which were deeply invasive. In fact, 46% of pT3 cancers present ≤1 mm from a serosal tissue reaction were associated with cancer in cytologic preparations from the serosa, which was comparable to pT4a tumors (55%).

They conclude that cytologic smears improve detection of peritoneal penetration among pT3 tumors compared with histology alone.

Tumors close (≤1 mm) to a fibroinflammatory tissue reaction on the serosa are likely associated with peritoneal involvement by cancer.

Peritumoral abscesses that communicate with the serosa and hemorrhage or fibrin on the serosa also predict cancer involvement of the peritoneum.

The presence of these findings among deeply invasive cancers should prompt their classification as pT4a lesions.



- Histologic Features and Cytologic Techniques That Aid Pathologic Stage Assessment of Colonic Adenocarcinoma. Panarelli NC, Schreiner AM, Brandt SM, Shepherd NA, Yantiss RK. Am J Surg Pathol. 2013 Jun 14. PMID: 23774176