tumoral deposits

Definition: Cancer foci having no histologic evidence of lymph node structure.

Tumor deposits: AJCC 8th Edition defintion :
 Tumor focus in the pericolic/perirectal fat or in adjacent mesentery within the Iymph drainage area of the primary tumor, but without identifiable Iymph node or vascular structure
 If vessel wall or its remnant identified (H&E, elastic, or any other stain), it should be classified as vascular (venous) invasion
 Tumor focus in or around a large nerve should be classified as PNI

Note: do not count a tumor deposit if there is nerve or vessel around focus. Count as perineural invasion or lymphatic vascular invasion.

Isolated cancer foci observed in fatty tissue attached to lymph nodes are treated as tumor deposit, irrespective of the nodal state, although extracapsular direct extension of the tumor is classified in nodal involvement. The maximum diameter of tumor deposit can be measured on the slide.

In routine practice, tumor deposits are observed in specimens sent for pathologic examination as "lymph nodes." There are also terms relating to cancer deposits with no residual lymph node structure: "mesorectal deposit," "mesenteric implants," "extrabowel skipped cancer infiltration," "extranodal cancer deposit," "tumor nodule," and "pericolonic tumor deposits."

Paty et al[1994] first showed the prognostic significance of such lesions; eg, mesenteric implants were reported to be associated with increased risk for pelvic recurrence in patients with rectal cancer who had undergone low anterior resection with coloanal anastomosis.

Goldstein and Turner[2000] believed that the number and greatest dimension of pericolonic tumor deposits should be reported separately from lymph node metastases.

Tumor deposits have been defined as all types of isolated cancer lesions having no residual lymph node structure observed in lymphadenectomy specimens, ie, tumor deposits apparently not associated with lymph node involvement, tumor nodules that might be related to a ruined lymph node, and tiny cancer foci in the lymphatic channels, blood vessels, or perineural space.

In a study, 20% of patients with advanced colorectal cancer who underwent potentially curative surgery were found to have tumor deposits.

Ueno and Mochizuki[1997] and Ueno et al[1998] previously demonstrated that tumor deposit has clinical significance as a strong prognosticator independent of tumor depth or nodal involvement in patients with curatively resected advanced rectal cancer and in patients with colorectal cancer who underwent operation for lung metastasis.[2003]

Aggressive tumor deposits

Tumor cells in aggressive tumor deposits, which have succeeded in their discontinuous spread, presumably through lymphatic or venous channels, and developed a tumor nodule, seem to be able to use new routes (blood vessels or the perineural space) for further development. The morphologic features of aggressive tumor deposits suggest that it could be a satellite lesion for systemic dissemination.

Although aggressive tumor deposits are observed in only 7% of the cases, it has the distinction of being an independent prognostic fator of a very disappointing survival outcome: the 5-year survival rate of patients with aggressive tumor deposits was calculated at only 29.8%.

Many pathologic parameters with prognostic significance, ie, cancer-related parameters (eg, tumor grade, cancer growth pattern, and tumor budding) and host-related parameters (eg, tumor-infiltrating lymphocytes, Crohn-like lymphoid reaction, and fibrotic cancer stroma), have been reported in colorectal cancer.

However, there are few parameters that can be used to select a patient group with a worse prognosis than that of patients with aggressive tumor deposits. With respect to the number of positive lymph nodes, eg, which is one of the most reliable prognosticators, patients with 9 or more positive nodes (only 1.5% of patients in the present cohort) had a 5-year survival rate of no less than 38.9%. Many investigators have noted that venous invasion and neural invasion observed in the primary tumor are prognostic indicators.

However, it is obvious that the prognostic impact of venous and neural invasion identified in the actively invasive frontal region of tuor deposits is much higher than that of these histologic features observed in the primary lesion.

Localization

 mesorectum

• The existence of isolated tumor deposits in the mesorectum was well demonstrated by microscopic examination with serial transverse sections of the mesorectum made as reported by Scott et al. [1995] and Reynolds et al. [1996]

Classification

Tumor deposits are divided into 2 types:
 with smooth contours, indicating that it originated in lymph node metastasis,
 with irregular contours, according to the TNM definition (6th edition).

In addition, tumor deposit is classified into the foci mostly confined to a vascular (lymphatic or venous vessel) space (vascular invasion type [VAS]) and cancer foci other than vascular invasion (non-VAS).

Non-VAS developing into a tumor nodule accompanied by venous and/or neural invasion in its actively invasive region was designated as aggressive tumor deposit.

Aggressive tumor deposit is defined as non-vascular invasion-type tumor deposit developing into a tumor nodule in which venous invasion (A) or neural invasion (B) is observed in an actively invasive region.

Open References

 An Interobserver Variability Study of Lymph Nodes and Pericolonic Tumor
Deposits in Colonic Adenocarcinoma. 2016
http://www.archivesofpathology.org/doi/pdf/10.5858/arpa.2013-0166-OA

 Extramural cancer deposits without nodal structure in colorectal cancer: optimal categorization for prognostic staging. Ueno H, Mochizuki H, Hashiguchi Y, Ishiguro M, Miyoshi M, Kajiwara Y, Sato T, Shimazaki H, Hase K. Am J Clin Pathol. 2007 Feb;127(2):287-94. PMID: 17210518

 Extramural Cancer Deposits Without Nodal Structure in Colorectal Cancer: Optimal Categorization for Prognostic Staging. American Journal of Clinical Pathology, 2007. http://www.medscape.com/viewarticle/551681

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