Histologic Tumor Grading

Independent of tumor stage, tumor grade is an important predictor of disease outcome with higher grade tumors behaving more aggressively. Grade is usually based on microscopic features, including nuclear features. The more closely the tumor resembles normal tissue, the lower the tumor grade and the less aggressive it will behave. Lower grade tumors generally grow more slowly and are less likely to spread and metastasize than are higher grade tumors. At some tumor sites, patients with higher grade tumors may receive more aggressive treatment regimens than patients with lower grade tumors.

Three types of grade can be recorded by registrars:

  • Clinical
  • Pathological: assigned when the tumor has been resected prior to chemotherapy or radiation therapy
  • Post-therapy: assigned when patient has received neoadjuvant (prior to surgical resection) therapy (chemotherapy or radiation therapy)

Grading Tips:

  • Assign the highest grade from the primary tumor for the clinical, pathological, or post-therapy timeframe as appropriate for the individual grade data item being coded.
  • All borderline tumors have a “/1” behavior code and are graded as GB: Grade Borderline (“B”).
    • Note: Borderline ovarian tumors are not reportable to SEER. These tumors may be collected by registries if desired.
  • For coding, clinical and pathological grade must not be blank. Code 9 if the primary tumor grade is not documented. Post-therapy grade may be left blank when it does not apply to the case.

The following ovarian tumor types are not customarily graded by pathologists.  If a grade is provided, then the registrar should assign the grade provided; otherwise, the case should be assigned Grade cannot be assessed/Unknown (“9”):

  • Clear cell carcinoma (High grade by definition)
  • Carcinosarcomas (Malignant Mixed Mullerian Tumors, MMMT)
  • Malignant sex-cord stromal tumors

For ovarian, fallopian tube, and primary peritoneal carcinomas, type of grading scheme depends on the type of tumor histology as outlined in tables below.

Epithelial Carcinomas

Note: No conversions are required for registrars to code grade.

Grading of Serous Ovarian Carcinomas
Grade Coding Morphology
Low grade (L) Better resemble normal cells than High grade tumors
High grade (H) Abnormal morphology
>3-fold nuclear size variation

FIGO System (International Federation of Gynecologists and Obstetricians): Endometrioid carcinomas are graded based on percentage of non-squamous, solid growth in tumor.

Grading of Endometrioid Ovarian Carcinomas
Grade Coding Differentiation Percentage of Non-squamous, Solid Growth
G1 (1) Well differentiated ≤5%
G2 (2) Moderately differentiated 6 to 50%
Grade 1 tumors with notable nuclear atypia
G3 (3) Poorly differentiated

WHO Grading System: While there is no grading scheme for other ovarian carcinomas, such as mucinous ovarian tumors, the following grading scheme can be used. Although choices are similar to FIGO, the WHO grading system is not based on percentage of non-squamous, solid growth pattern.

Grading of Other Ovarian Carcinomas (Ex: Mucinous)
Grade Coding Differentiation
G1 (1) Well differentiated
G2 (2) Moderately differentiated
G3 (3) Poorly differentiated
GX (9) Grade cannot be assessed

Germ Cell Tumors

Immature teratomas are coded by a 2-tier system according to the Grade Coding Instructions and Tables Manual. https://www.naaccr.org/SSDI/Grade-Manual.pdf?v=1526066371External Website Policy.

Note: No conversions are required for registrars to code grade.

Grading of Immature Teratomas ’ 2-Tier System
2-Tier System Quantity of Immature/Embryonal Elements*
Low Grade (L) <1
High Grade (H) 1 to <4
Grading of Immature Teratomas ’ 3-Tier System
3-Tier System Quantity of Immature/Embryonal Elements*
G1 (1) <1
G2 (2) 1 to <4
G3 (3) ≥4

* Measured as number of immature/embryonal elements (commonly neuroectodermal tissue) at low power [40x objective] on any slide.

Sertoli-Leydig Cell Tumors

Grading of Sertoli-Leydig Cell Tumors
3-Tier System Differentiation Histomorphology
Grade 1 (1) Well Sertoli cells in open/closed tubules
Grade 2 (2) Intermediate Sertoli cells in lobular aggregates
Grade 3 (3) Poorly Sarcomatous sheets of stroma
Only focal lobulated Sertoliform growth

For additional details of grade coding, refer to Grade Coding Instructions and Tables Manual on the NAACCR website: https://www.naaccr.org/SSDI/Grade-Manual.pdf?v=1526066371External Website Policy.

Updated: June 8, 2018