Appendiceal NET Grading

WHO/ENETS G1–G3 grading with higher-grade-prevails logic and a live decision matrix.

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This calculator is a pathology decision-support and educational tool for mathematical normalization of mitotic counts and application of established appendiceal NET proliferation grading criteria. It does not replace the current WHO classification, ENETS guidance, CAP protocol, institutional protocol, or professional pathologist judgment. Always verify the applicable current classification and reporting requirements before issuing a diagnostic report.

Reference

Grading thresholds

Exact thresholds, tested unrounded. 1.99 → G1 range; 2.00 → G2 range; 20.00 → G2 range; 20.01 → G3 range. The same applies to Ki-67 at 3% and 20%. Rounding is never used to determine the grade.

Grade	Mitoses / 2 mm²	Ki-67
G1	< 2	< 3%
G2	2 – 20	3 – 20%
G3	> 20	> 20%

Decision matrix — final grade is the higher of the two

Final grade = max(mitotic grade, Ki-67 grade). The two grades are never averaged.

Mathematical field-area conversion

A = π(d/2)²

Total area = A × N

Mitoses/2 mm² = (M × 2) ÷ (A × N)

HPFs for 10 mm² = 10 ÷ A · HPFs ≈ 2 mm² = 2 ÷ A

Final grade = max(mitotic grade, Ki-67 grade)

The field-area conversion is a mathematical standardization calculation, not an independent grading criterion. It produces the mitoses/2 mm² value to which the grading criteria are then applied.

40× magnification alone does not define a universal HPF area. The actual microscope field diameter must be used because field area varies between microscopes.

Field diameter reference table

Generated from the formula, not stored values.

Field diameter	HPF area (mm²)	HPFs for 10 mm²	HPFs ≈ 2 mm²
0.40 mm	0.1257	≈80	≈15.9
0.41 mm	0.1320	≈76	≈15.1
0.42 mm	0.1385	≈72	≈14.4
0.43 mm	0.1452	≈69	≈13.8
0.44 mm	0.1521	≈66	≈13.2
0.45 mm	0.1590	≈63	≈12.6
0.46 mm	0.1662	≈60	≈12.0
0.47 mm	0.1735	≈58	≈11.5
0.48 mm	0.1810	≈55	≈11.1
0.49 mm	0.1886	≈53	≈10.6
0.50 mm	0.1963	≈51	≈10.2
0.51 mm	0.2043	≈49	≈9.8
0.52 mm	0.2124	≈47	≈9.4
0.53 mm	0.2206	≈45	≈9.1
0.54 mm	0.2290	≈44	≈8.7
0.55 mm	0.2376	≈42	≈8.4
0.56 mm	0.2463	≈41	≈8.1
0.57 mm	0.2552	≈39	≈7.8
0.58 mm	0.2642	≈38	≈7.6
0.59 mm	0.2734	≈37	≈7.3
0.60 mm	0.2827	≈35	≈7.1
0.61 mm	0.2922	≈34	≈6.8
0.62 mm	0.3019	≈33	≈6.6
0.63 mm	0.3117	≈32	≈6.4
0.64 mm	0.3217	≈31	≈6.2
0.65 mm	0.3318	≈30	≈6.0
0.66 mm	0.3421	≈29	≈5.8
0.67 mm	0.3526	≈28	≈5.7
0.68 mm	0.3632	≈28	≈5.5
0.69 mm	0.3739	≈27	≈5.3

Counting mitoses

Count only clearly identifiable mitoses. Do not count apoptotic nuclei, karyorrhectic nuclei, hyperchromatic nuclei, degenerative nuclear changes, or ambiguous nuclear fragments. Identify the appropriate mitotically active area/hotspot for assessment.

Precision handling around thresholds

The HPF area is never rounded before being used, and grade thresholds are tested against the unrounded rate. This matters most near 2 and 20 mitoses/2 mm²: a rate of 1.996 displays as "2.0" but is below 2 and therefore in the G1 range. Where the rounded display could disagree with the threshold test, the calculator states the exact value and which side of the threshold it falls on.

Missing data behaviour

If only one parameter is available, its grade is still determined and used, and the calculator states plainly that the other could not be determined. A tumor is never classified G1 when the available parameter sits in the G2 or G3 range.

Grade is not risk stratification

The G1/G2/G3 proliferation grade is separate from overall risk assessment. Size, location, mesoappendiceal, lymphovascular and perineural invasion, margins, nodal and distant metastatic status are documented separately and do not alter the grade.

Sources

WHO Classification of Tumours — current applicable volume for digestive system / appendiceal neuroendocrine neoplasms.

ENETS / WHO neuroendocrine tumor grading framework, based on mitotic count per 2 mm² and Ki-67 proliferation index, with the higher grade indicated by either parameter determining the final grade.