Site-Specific Factor 4

Mitotic Count

Notes

**Note 1:** The mitotic count, the number of mitoses per 10 high-power fields (HPF), is an element in a proposed grading scheme for neuroendocrine tumors (NETs) of the gastrointestinal system. This site-specific factor presumes the denominator of 10 HPF, so just the numberator (the mitotic count) is coded here. For other schemas in which mitotic count is collected, the denominator may vary. **Note 2:** As described in the AJCC chapter on NETs, 10 HPF at a magnification objective of 40 (40x) are equivalent to 2 square millimeters (mm). (1) **Note 3:** Record mitotic count to the nearest tenth as documented in the pathology report. For example, a mitotic count of 3/10 HPF would be coded as 030. **Note 4:** Code the specific mitotic count only per 10 HPF or 2 square mm; assume the denominator is 10 HPF or 2 square mm if not specified. Use code 996 only if the mitotic count is expressed with a specific denominator other than 10 HPF or 2 square mm.

Default

988

NAACCR Item

NAACCR #2910
Code Description
000 0.0 mitoses per 10 high-power fields (HPF) (40x field)
0.0 mitoses per 2 square millimeters (mm)
Mitoses absent
No mitoses present
001-008 01 - 0.8 mitosis per 10 HPF (40x field)
0.1 - 0.8 mitosis per 2 square mm
009 0.9 mitosis per 10 HPF (40x field)
0.9 mitosis per 2 square mm

Stated as less than 1 mitosis per 10 HPF (40x field)
Stated as less than 1 mitosis per 2 square mm
010-500 1-50 mitoses per 10 HPF (40x field)
1-50 mitoses per 2 square mm
510 51 or more mitoses per 10 HPF (40x field)
51 or more mitoses per 2 square mm
988 Not applicable: Information not collected for this case
990 Specific number not stated, described as less than 2 mitoses per 10 HPF (40x field)
Specific number not stated, described as less than 2 mitoses per square mm

Stated as low mitotic count or rate with no specific number
991 Specific number not stated, described as between 2 and 20 mitoses per 10 HPF (40x field)
Specific number not stated, described as between 2 and 20 mitoses per 2 square mm
992 Specific number not stated, described as more than 20 mitoses per 10 HPF (40x field)
Specific number not stated, described as more than 20 mitoses per 2 square mm

Stated as high mitotic count or rate with no specific number
996 Mitotic count described with denominator other than 10 HPF (40x field) or 2 square mm
998 No histologic examination of primary site
999 Unknown or no information
Not documented in patient record
(1) American Joint Committee on Cancer., & Edge, S.B. (2010) *AJCC Cancer Staging Manual (7th ed.)*. New York; London: Springer, pg. 184