Tumour deposit

A tumour deposit is a microscopic or macroscopic tumour nodule in the lymphatic drainage bed of the (primary) tumour. The term is applied in colorectal adenocarcinoma and has also been described in gastric cancer.

It is also known as discoutinuous extramural extension and peritumoural deposit.

Conceptually, tumour deposits are like the in-transit metastases of malignant melanoma and dermatopathology; however, it is important to note that on a practical level the specific (morphologic/clinical) definitions of tumour deposit and in-transit metastasis are different.

General

Significance:

• Poor prognosticator.
  • Can be understood as a type of invasive front/border, e.g. well-circumscribed border versus infiltrative border.

Definition

Definition - TNM/AJCC 7th edition:

• Microscopic or macroscopic nodule in the lymphatic drainage bed of the tumour.
  • No standardized distance (from tumour) criteria are defined.
• No findings suggestive of it being a lymph node replaced by tumour:
  1. No significant lymphoid tissue.
  2. Irregular contour.
     • Round nodules of tumour are considered lymph nodes that are replaced by tumour.

Notes:

• The definition of tumour deposit has changed significantly between the TMN/AJCC fifth, sixth and seventh editions.
• Lesions that are not in the drainage bed of tumour are metastatic disease, pM1b.

Ueno criteria

Ueno et al. propose that a tumour deposit is either:

1. >=2 mm from the tumour front.
2. >=2 mm (radially) from the deepest aspect of the muscularis propria, if the tumour is not present in the plane of section.

Staging

Staging implications in colorectal cancer:

• Tumour deposits are not counted as (positive) lymph nodes and in the context of positive lymph nodes do not change the N stage.
  • If no positive lymph nodes are present, the N stage is pN1c.
• The T stage is not affected by tumour deposits.

See also

• Colorectal carcinoma.
• Metastasis.