Collaborative Stage

Note 1: The mitotic rate (the count of mitoses per 50 high-power fields or 50 HPF) reflects the potential aggressiveness or prognosis of gastrointestinal stromal tumors (GIST), and is used alone to determine their histologic grade (low or high). The mitotic rate is also a factor in assigning the AJCC 7 anatomic stage/prognostic group. This site-specific factor presumes the denominator of 50 HPF or its equivalent, so just the numerator (the mitotic count) is coded here.
Note 2: A HPF usually has a magnification objective of 40 (a 40x field). As described in the AJCC chapter on GIST, 50 HPF are equivalent to viewing a total area of 5 square millimeters (mm) at 40x magnification.
Note 3: Record mitotic count, to the nearest tenth of a mitosis, as documented in the pathology report. For example, a mitotic count of 6/50 HPF, or 6 per 5 square mm, would be coded 060.
Note 4: Code the specific mitotic count only per 50 HPF or 5 square mm; assume the denominator is 50 HPF or 5 square mm if not specified. Use code 996 only if the mitotic count is expressed with a specific denominator other than 50 HPF or 5 square mm.

Code	Description
000	0.0 mitoses per 50 HPF (40x fields) 0.0 mitoses per 5 square mm Mitoses absent No mitoses present
001-008	0.1 - 0.8 mitoses per 50 HPF (40x fields) 0.1 - 0.8 mitoses per 5 square mm
009	0.9 mitoses per 50 HPF (40x fields) 0.9 mitoses per 5 square mm Stated as less than 1 mitosis per 50 HPF (40x fields) Stated as less than 1 mitosis per 5 square mm
010-100	1 - 10 mitoses per 50 HPF (40x fields) 1 - 10 mitoses per 5 square mm
110	11 or more mitoses per 50 HPF (40x fields) 11 or more mitoses per 5 square mm
888	OBSOLETE DATA CONVERTED V0200 See code 988 Not applicable for this site
988	Not applicable:Information not collected for this case (May include cases converted from code 888 used in CSv1 for "Not applicable" or when the item was not collected. If this item is required to derive T, N, M, or any stage, use of code 988 may result in an error.)
990	Specific number not stated, described less than or equal to 5 mitoses per 50 high-power fields (40x field) Specific number not stated, described less than or equal to 5 mitoses per 5 square millimeters
991	Specific number not stated, described as more than 5 mitoses per 50 HPF (40x fields) Specific number not stated, described as more than 5 mitoses per 5 square mm Stated as high mitotic count or rate with no specific number
995	OBSOLETE DATA CONVERTED V0203 See code 991 Specific number not stated, described as greater than 5 mitoses per 50 high-power fields (40x field) Specific number not stated, described as greater than 5 mitoses per 5 square millimeters
996	Mitotic count described with denominator other than 50 HPF (40x field)/5 square mm
998	No histologic specimen from primary site
999	Unknown or no information Not documented in patient record

GISTPeritoneum

CS Site-Specific Factor 5
Mitotic Count

GISTPeritoneum

CS Site-Specific Factor 5Mitotic Count

CS Site-Specific Factor 5
Mitotic Count