Potential pitfalls concerning colorectal cancer classification in the seventh edition of the AJCC Cancer Staging Manual, Ratto C, Ricci R., Dis Colon Rectum. 2011 Aug;54(8):e232.
The seventh edition of the AJCC Cancer Staging Manual1 has introduced the new site-specific factor tumor deposits (TDs) in colorectal cancer staging, recognizing its prognostic value.2-5 TDs are “discrete foci of tumor found in the pericolic or perirectal fat or in adjacent mesentery (mesocolic fat) away from the leading edge of the tumor and showing no evidence of residual lymph node tissue but within the lymph drainage area of the primary carcinoma.” They “may represent discontinuous spread, venous invasion with extravascular spread (V1/V2), or a totally replaced lymph node (N1/N2).” “Their number should be recorded in the site-specific Prognostic Markers on the staging form as Tumor Deposit (TD).” It is recommended that “the nodule is recorded in the TD category and as a N1c positive node”; N1c is defined as “tumor deposit(s) in the subserosa, mesentery, or nonperitonealized pericolic or perirectal tissues without regional nodal metastasis.” Finally, after a reminder that “a satellite peritumoral nodule in the pericolorectal adipose tissue of a primary carcinoma without histological evidence of residual lymph node in the nodule may represent discontinuous spread, venous invasion with extravascular spread (V1/V2), or a totally replaced lymph node (N1/N2),” a note recommends that “replaced nodes should be counted separately in the N category, whereas discontinuous spread or venous invasion should be classified and counted in the Site-Specific Factor category Tumor Deposits (TD).”
N1c forces into the N category the “non N type” of TDs, but this can be accepted for practical purposes. However, some incongruities remain. First, the N state of a case with TDs only would be N1c, whereas a case with TDs and 1 to 3 positive “true” lymph node(s) would paradoxically “regress” to N1a/b. Second, why are totally replaced lymph nodes first recognized as one of the variants of TDs, and then requested to be considered separately in the N category? The identification of replaced lymph nodes depends on arbitrary criteria, formerly the size (TNM fifth edition),6 and later the shape (TNM sixth and seventh editions).7,1 In keeping with the general rule postulated in the chapter concerning “Purposes and Principles of Cancer Staging” (“tumor nodule with smooth contour in regional node area classified as positive node”), totally replaced lymph nodes identified by their smooth contour should be unequivocally excluded from TD variants (recalling the definition of “totally replaced lymph node” in the chapter concerning colorectal cancer); alternatively, they should be considered and counted together with the other TDs.
Thus, the seventh edition of the AJCC Cancer Staging Manual uses some confounding terms concerning colorectal cancer; the resulting incongruities urge a clarification.