Deciphering Your Pathology and Stage

Pathology and staging have undergone a revolution in recent years. While doctors used to rely solely on what they could see under a microscope, standard care now recommends using the tumor’s genetic “fingerprint” to create a more precise roadmap for your care. The FIGO 2023 staging system integrates these molecular findings with traditional surgical results ^[1].

The Four Molecular Subtypes

Your pathology report should ideally include a molecular classification. These tests look at the tumor’s DNA, not necessarily your inherited genetics (with one important exception discussed below). This tells us about the biology of the tumor—how it behaves and how it might respond to treatment ^[2].

1. POLE-mutated: These tumors have a specific mutation in the POLE gene. While they may appear fast-growing under a microscope, they generally have an excellent prognosis ^[3]. Because they are so biologically favorable, having this mutation can actually “downstage” an early cancer ^[1].
2. MMRd (Mismatch Repair Deficient): These cells have lost the ability to fix DNA errors. This subtype is important for two reasons: it may respond very well to immunotherapy, and it can be a sign of Lynch syndrome, an inherited genetic condition ^[4][5].
3. NSMP (No Specific Molecular Profile): This is the most common group. These tumors don’t have the other markers, and their behavior is usually predicted by traditional factors like how deep the cancer grew into the muscle ^[3][6].
4. p53-abnormal: This is considered the most aggressive subtype. Because these tumors are more likely to spread, finding this profile can “upstage” an early cancer even if it appears limited to the uterus ^[1][3].

Traditional Pathology Terms

Even with molecular testing, traditional “look-and-see” pathology remains vital:

• Histology: This is the cell type. Endometrioid is the most common and often less aggressive. Serous, Clear Cell, and Carcinosarcoma are classified as “aggressive histologies” in the new FIGO system ^[1][7].
• Grade: This describes how much the cancer cells look like normal tissue. Grade 1 (low-grade) looks more normal; Grade 3 (high-grade) looks very different and grows faster ^[8].
• Myometrial Invasion: This measures how deep the cancer has grown into the myometrium (the muscular wall of the uterus). Invasion of more than 50% increases the risk of the cancer spreading to lymph nodes ^[8][9].
• LVSI (Lymphovascular Space Invasion): This tells us if cancer cells have found their way into the small “pipes” (lymph or blood vessels) within the uterine wall. FIGO 2023 now distinguishes between focal (less than 5 vessels) and substantial (5 or more vessels), with substantial LVSI being a higher risk factor ^[1][10].

FIGO 2023: An Integrated Stage

Your “stage” (I through IV) describes how far the cancer has spread anatomically. What is new is that your molecular subtype can modify that stage in early disease ^[1]. For example:

• An early-stage tumor that is confined to the uterus but has a p53-abnormal profile may be upstaged to Stage IIC because of the higher risk ^[1].
• An early-stage tumor with a POLE mutation may be considered very low risk (Stage IA) even if it has deeper muscle invasion ^[1].
  Note: Molecular staging notation is complex. Your final stage must be assigned from your complete surgical and pathology findings.

Lynch Syndrome: Why MMR Testing Matters

Many current guidelines recommend universal screening for every endometrial cancer patient using MMR (Mismatch Repair) or MSI testing ^[5].

• The Goal: To see if your cancer was caused by Lynch syndrome, which increases the risk of other cancers (like colon cancer) for you and your family ^[5][11].
• The Pathway: If your tumor is “MMRd” (specifically showing loss of MLH1/PMS2), the lab will often perform a follow-up test called MLH1 promoter methylation. If that test is negative, it strongly suggests Lynch syndrome, and you should be referred to a genetic counselor for a blood test ^[12][13]. If the tumor shows loss of MSH2, MSH6, or isolated PMS2, this usually leads directly to a genetics referral.

Checklist: Is Your Pathology Report Complete?

A modern, actionable pathology report should ideally include all of the following:

• [ ] Histologic Type (e.g., Endometrioid, Serous) ^[1]
• [ ] Grade (1, 2, or 3) ^[8]
• [ ] Depth of Myometrial Invasion (e.g., <50% or >50%) ^[1]
• [ ] LVSI Status (None, Focal, or Substantial) ^[1]
• [ ] MMR/MSI Status (for Lynch screening and immunotherapy) ^[5]
• [ ] p53 Status (Normal/Wild-type or Abnormal/Mutant) ^[1]
• [ ] POLE Mutation Status (Pathogenic mutation present or absent) ^[1]
• [ ] Cervical Stromal Invasion (Whether it has spread to the neck of the uterus) ^[1]
• [ ] Lymph Node Status (If nodes were removed, were they positive for micrometastasis or macrometastasis?) ^[1]