In a patient with endometrial cancer that has 0.9 cm myometrial invasion (less than 50 % of the myometrium) with extensive adenomyosis and positive lymph‑vascular space invasion, what FIGO stage is appropriate (IA, IB, IIA, or IIB)?

Endometrial Cancer Staging: Stage IA

This patient has FIGO Stage IA endometrial cancer. The tumor demonstrates <50% myometrial invasion (0.9 cm invasion with 3.8 cm residual myometrium), which by definition classifies it as Stage IA regardless of LVSI status or the presence of adenomyosis 1, 2.

Staging Rationale

Primary Staging Criterion: Myometrial Invasion Depth

• Stage IA is defined as tumor confined to the corpus uteri with <50% myometrial invasion 1, 2
• Stage IB is defined as tumor with ≥50% myometrial invasion 1, 2
• In this case, 0.9 cm invasion into 4.7 cm total myometrium (0.9 + 3.8) equals approximately 19% invasion, clearly <50% 1
• Stage II requires cervical stromal invasion, which is not present in this case 1, 2

Why LVSI Does Not Change the Stage

• Positive LVSI does not upstage disease from IA to a higher stage in the 2009 FIGO system 1
• LVSI is a critical prognostic factor for risk stratification and treatment planning, but it does not alter the anatomic stage 1
• The 2023 FIGO staging update proposes that substantial LVSI would be classified as Stage IIB, but this system is pending broader validation and the 2009 system remains the current standard 2, 3

The Adenomyosis Confounder

Extensive adenomyosis creates significant challenges in accurately measuring myometrial invasion depth, but does not change how staging is determined 4:

• Adenomyosis reduces the accuracy of imaging and pathologic assessment by decreasing contrast between tumor and myometrium 4
• The depth of invasion should be measured from the endometrial-myometrial junction to the deepest point of tumor invasion, excluding adenomyosis foci when possible 4
• When cancer involves adenomyotic foci deep in the myometrium but the surface tumor shows <50% invasion, staging should be based on the surface tumor invasion depth 4, 5
• Cancer-positive adenomyosis is associated with higher risk of deep myometrial invasion (34.8% vs 6.4% outer half invasion), but this represents biological behavior rather than a staging criterion 5

Risk Stratification Despite Stage IA Classification

While this patient is Stage IA, the presence of positive LVSI significantly elevates recurrence risk 1:

• Stage IA with positive LVSI cannot be classified as "low risk" 1
• This patient would be classified as intermediate or high-intermediate risk depending on tumor grade 1
• Risk stratification guides decisions about lymph node assessment and adjuvant therapy, even though the anatomic stage remains IA 1

Common Pitfalls to Avoid

• Do not upstage to IB based on adenomyosis involvement alone—measure invasion from the endometrial surface 4, 5
• Do not confuse risk stratification with staging—LVSI increases risk but does not change the stage from IA in the current 2009 FIGO system 1
• Do not apply the 2023 FIGO staging criteria (which would classify substantial LVSI as Stage IIB) until it becomes the validated standard 2, 3
• Ensure pathologists clearly document whether myometrial invasion measurements account for adenomyosis, as this affects accuracy 4