TNM Classification, Histologic Grade, Prognostic Stage, and Risk Stratification

The American Joint Committee on Cancer tumor/node/metastasis (TNM) classification for gastrointestinal stromal tumors (GISTs) is provided below, along with anatomic stage/prognostic groups.^[1]

Table 1. TNM classification of gastrointestinal stromal tumors (Open Table in a new window)

Primary tumor (T)
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor
T1	Tumor ≤ 2 cm
T2	Tumor > 2 cm but ≤ 5 cm
T3	Tumor > 5 cm but ≤ 10 cm
T4	Tumor > 10 cm in greatest dimension
Regional lymph nodes (N)
N0	No regional lymph node metastasis
N1	Regional lymph node metastasis
Distant metastasis (M)
M0	No distant metastasis
M1	Distant metastasis

Table 2. Histologic grade (Open Table in a new window)

Histologic grade (G)
GX	Grade cannot be assessed
G1	Low grade; mitotic rate 5/50 per high-power field (HPF) or less
G2	High grade; mitotic rate > 5/50 HPF

Table 3. Anatomic stage/prognostic groups for gastric and omental GISTs (Open Table in a new window)

Stage	T	N	M	Mitotic rate
IA	T1 or T2	N0	M0	Low mitotic rate
IB	T3	N0	M0	Low mitotic rate
II	T1	N0	M0	High mitotic rate
	T2	N0	M0	High mitotic rate
	T4	N0	M0	Low mitotic rate
IIIA	T3	N0	M0	High mitotic rate
IIIB	T4	N0	M0	High mitotic rate
IV	Any T	N1	M0	Any rate
IV	Any T	Any N	M1	Any rate

Table 4. Anatomic stage/prognostic groups for small intestinal, esophageal, colorectal, mesentric, and peritoneal GISTs (Open Table in a new window)

Stage	T	N	M	Mitotic rate
I	T1 or T2	N0	M0	Low mitotic rate
II	T3	N0	M0	Low mitotic rate
IIIA	T1	N0	M0	High mitotic rate
IIIA	T4	N0	M0	Low mitotic rate
IIIB	T2	N0	M0	High mitotic rate
	T3	N0	M0	High mitotic rate
	T4	N0	M0	High mitotic rate
IV	Any T	N1	M0	Any rate
IV	Any T	Any N	M1	Any rate

The decision whether to pursue adjuvant treatment depends on an estimation of risk of recurrence, which is typically based on the following factors^{[2, 3]}:

Tumor size
Mitotic index
Location within the GI tract
Presence or absence of tumor rupture

Yang et al reported that the mitotic index in GISTs can be reliably predicted with the use of a magnetic resonance imagimg texture-based model.^[4]

Table 5. Modified National Institutes of Health risk stratification criteria for GIST (Open Table in a new window)

Risk category	Tumor size (cm)	Mitotic index (per 50 HPFs)	Primary tumor site
Very low risk	< 2.0	≤ 5	Any
Low risk	2.1 to 5.0	≤ 5	Any
Intermediate risk	2.1 to 5.0	> 5	Gastric
	< 5.0	6 to 10	Any
	5.1 to 10.0	≤ 5	Gastric
High Risk	Any	Any	Any, with tumor rupture
	> 10	Any	Any
	Any	> 10	Any
	> 5	> 5	Any
	2.1 to 5.0	> 5	Nongastric
	5.1 to 10.0	≤ 5	Nongastric

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Table 1. TNM classification of gastrointestinal stromal tumors

Primary tumor (T)
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor
T1	Tumor ≤ 2 cm
T2	Tumor > 2 cm but ≤ 5 cm
T3	Tumor > 5 cm but ≤ 10 cm
T4	Tumor > 10 cm in greatest dimension
Regional lymph nodes (N)
N0	No regional lymph node metastasis
N1	Regional lymph node metastasis
Distant metastasis (M)
M0	No distant metastasis
M1	Distant metastasis

Table 2. Histologic grade

Histologic grade (G)
GX	Grade cannot be assessed
G1	Low grade; mitotic rate 5/50 per high-power field (HPF) or less
G2	High grade; mitotic rate > 5/50 HPF

Table 3. Anatomic stage/prognostic groups for gastric and omental GISTs

Stage	T	N	M	Mitotic rate
IA	T1 or T2	N0	M0	Low mitotic rate
IB	T3	N0	M0	Low mitotic rate
II	T1	N0	M0	High mitotic rate
	T2	N0	M0	High mitotic rate
	T4	N0	M0	Low mitotic rate
IIIA	T3	N0	M0	High mitotic rate
IIIB	T4	N0	M0	High mitotic rate
IV	Any T	N1	M0	Any rate
IV	Any T	Any N	M1	Any rate

Table 4. Anatomic stage/prognostic groups for small intestinal, esophageal, colorectal, mesentric, and peritoneal GISTs

Stage	T	N	M	Mitotic rate
I	T1 or T2	N0	M0	Low mitotic rate
II	T3	N0	M0	Low mitotic rate
IIIA	T1	N0	M0	High mitotic rate
IIIA	T4	N0	M0	Low mitotic rate
IIIB	T2	N0	M0	High mitotic rate
	T3	N0	M0	High mitotic rate
	T4	N0	M0	High mitotic rate
IV	Any T	N1	M0	Any rate
IV	Any T	Any N	M1	Any rate

Table 5. Modified National Institutes of Health risk stratification criteria for GIST

Risk category	Tumor size (cm)	Mitotic index (per 50 HPFs)	Primary tumor site
Very low risk	< 2.0	≤ 5	Any
Low risk	2.1 to 5.0	≤ 5	Any
Intermediate risk	2.1 to 5.0	> 5	Gastric
	< 5.0	6 to 10	Any
	5.1 to 10.0	≤ 5	Gastric
High Risk	Any	Any	Any, with tumor rupture
	> 10	Any	Any
	Any	> 10	Any
	> 5	> 5	Any
	2.1 to 5.0	> 5	Nongastric
	5.1 to 10.0	≤ 5	Nongastric