Revision 37 for 'Rectal cancer (staging)'

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Rectal cancer (staging)

Staging strongly influences the success of, and rate of local recurrence following rectal cancer resection. In rectal cancer, pre-treatment MRI is the evaluation of choice, guiding surgical and non-surgical management options. 

In select cases, preoperative post chemoradiation MRI followup is also a valuable tool at assessing attempted tumor downstaging (tumor response assessment) prior to deciding further management options.

TNM staging

See: TNM staging system for a general description.

Primary tumor staging (T)

Strictly speaking TMN staging, such as American Joint Committee on Cancer (AJCC) 7th ed, does not sub-classify T3. This is a feature of MRI staging but does have treatment and prognostic significance 7,8

  • Tx: primary tumor cannot be assessed
  • T0: no evidence of primary tumor
  • Tis: carcinoma in situ: intraepithelial or invasion of lamina propria
  • T1: tumor invades submucosa
  • T2: tumor invades muscularis propria
  • T3: tumor invades through the muscularis propria into the subserosa or into non-peritonealised perirectal tissues
    • T3a: tumor extends <1 mm beyond muscularis propria 4
    • T3b: tumor extends 1-5 mm beyond muscularis propria 4
    • T3c: tumor extends 5-15 mm beyond muscularis propria 4
    • T3d: tumor extends 15 mm beyond muscularis propria 4
  • T4: tumor invades directly into other organs or structures and/or perforates visceral peritoneum
    • T4a: tumor penetrates to the surface of the visceral peritoneum
    • T4b: tumor directly invades or is adherent to other organs or structures
Regional lymph nodes (N)

The size cut off for mesorectal nodes is usually taken at 5mm 6 

More recent analysis of data puts into question the importance of lymph nodes as a predictors of local recurrence and also questions the rational of size criteria for node assessment 9

  • Nx: regional nodes not assessed
  • N0: no regional lymph nodes
  • N1: metastasis in 1-3 regional (peri-rectal) lymph nodes
    • N1a: metastasis in one regional lymph node
    • N1b: metastasis in 2-3 regional lymph nodes
    • N1c: tumor deposit(s) in the subserosa, mesentery, or nonperitonealized pericolic or perirectal tissues without regional nodal metastasis
  • N2: metastasis in 4 or more regional lymph nodes
    • N2a: metastasis in 4-6 regional lymph nodes
    • N2b: metastasis in 7 or more regional lymph nodes
  • Mx: cannot be assessed
  • M0: no distant metastasis
  • M1: distant metastasis
    • M1a: metastasis confined to one organ or site (for example, liver, lung, ovary, nonregional node)
    • M1b: metastases in more than one organ/site or the peritoneum
Stage groupings
  • stage 0: Tis N0 M0
  • stage I: T1-2, N0 M0
  • stage II
    • IIa: T3, N0, M0
    • IIb: T4a, N0, M0
    • IIc: T4b, N0, M0
  • stage III
    • IIIa: T1-2, N1, M0
    • IIIb: T3-4, N1, M0
    • IIIc: T3-4b, N2, M0
  • stage IV: any T, any N M1
Additional prognostic indicators

The following are significant prognostic indicators, and should be commented on when staging rectal cancer with MRI, alongside the TNM stage:

  • extramural venous invasion (EMVI)
    • may be contiguous or non-contiguous
    • non-contigous deposits reflect N1c
    • imparts poor prognosis as a predictor of haematogenous spread
  • circumferential resection margin (CRM)
    • represented by the mesorectal fascia (MRF)
    • CRM positive if either tumor, involved lymph node, or EMVI (continous or discontinous) is within 1mm of the mesorectal fascia
    • peritoneal reflection does not constitute CRM, which if involved reflects at least stage T4a disease
Additional specific MRI imaging staging subsets of rectal tumor

Special consideration should be given to low rectal tumors as these carry a different prognosis from higher lesions. This is predominantly due to anatomical considerations including waist-like tapering of the mesorectum 10

Early rectal cancer and significant polyps may also be subclassified especially with use of good quality, high resolution T2-weighted MR images. This relies on the recognition that most rectal tumors (apart from mucinous tumors) have intermediate T2 signal compared to hyperintense submucosa and hypointense muscularis layers 9. Such staging may be helpful in selecting less extensive surgical resection options.

  • Low rectal tumor staging 10
    • Stage 1: Tumor confined to bowel wall with intact outer muscularis propria
    • Stage 2: Tumor replaces muscularis propria but does not extend into intersphincteric plane
    • Stage 3: Tumor invades intersphincteric plane or lies within 1mm of levator muscles
    • Stage 4: Tumor invades external anal sphincter and is within 1mm and beyond levators with or without invading adjacent organs
  • Early rectal tumor staging 9
    • T0/early T1sm1: no submucosa (sm) disruption evident with entire thickness of submucosal stripe preserved
    • T1sm2: at least 1mm of submucosa preserved
    • T1sm3/early T2: less than 1mm of submucosa preserved but full thickness of muscularis propria preserved
    • T2 early: more than 1mm muscularis propria preserved
    • T2/T3a: 0mm muscularis propria preserved / less than 1mm microscopic invasion beyond muscularis propria (prognosis identical)
    • T3b: 1-5mm invasion beyond muscularis propria (still carries good prognosis)

See also

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