What is the recommended treatment for a patient with stage 1A endometrial cancer, positive peritoneal (washings), and mixed mismatch repair (MMR) deficiency?

Treatment for Stage IA Endometrial Cancer with Positive Peritoneal Washings and Mixed MMR Deficiency

For stage IA endometrial cancer with positive peritoneal washings, the patient should be treated according to stage IIIA disease, which requires adjuvant pelvic radiotherapy or abdomino-pelvic radiotherapy following total hysterectomy with bilateral salpingo-oophorectomy. 1, 2

Critical Staging Clarification

The presence of positive peritoneal cytology fundamentally changes the stage and treatment approach:

• Positive peritoneal washings upstage the disease from stage IA to stage IIIA according to both the 1988 and 2009 FIGO staging systems 1
• Under the 1988 FIGO system, stage IIIA explicitly includes "positive peritoneal cytology" 1
• Under the 2009 FIGO system, stage IIIA includes "tumour invades serosa of the corpus uteri and/or adnexae" with positive cytology considered in this category 1

Surgical Management

The standard surgical approach should have included:

• Total hysterectomy with bilateral salpingo-oophorectomy 3, 4
• Pelvic and para-aortic lymphadenectomy for complete surgical staging, particularly given the upstaging to stage IIIA 4, 2
• Thorough exploration of the abdominal cavity including inspection of the liver, diaphragm, omentum, and peritoneal surfaces 1

Adjuvant Treatment for Stage IIIA Disease

The recommended adjuvant therapy options for stage IIIA disease with positive peritoneal cytology include:

• Postoperative pelvic radiotherapy as the primary option 2
• Abdomino-pelvic radiotherapy as an alternative approach 2
• Pelvic control is increased with pelvic radiotherapy in stage III disease 1

Important Caveat Regarding Historical Guidelines

Older guidelines (2008) suggested that "patients with stage III disease solely on the basis of positive peritoneal cytology are treated as patients with stage I or II disease, based on the other clinicopathological data" 1. However, this approach has been superseded by more recent recommendations that explicitly classify positive cytology as stage IIIA requiring adjuvant radiotherapy 2.

Role of MMR Deficiency

The mixed MMR deficiency status is an important prognostic and potentially therapeutic consideration:

• MMR deficiency may influence response to immunotherapy in advanced or recurrent disease, though this is not standard adjuvant treatment for stage IIIA
• The primary treatment decision remains based on stage IIIA classification regardless of MMR status 2

Chemotherapy Considerations

While not the primary adjuvant treatment for stage IIIA disease based solely on positive cytology:

• Combination chemotherapy with cisplatin and doxorubicin or carboplatin and paclitaxel may be considered for high-risk stage III disease 1, 2, 5
• Chemotherapy is typically reserved for more extensive stage III disease (such as IIIC with lymph node involvement) or stage IV disease 1

Common Pitfall to Avoid

Do not treat this patient as stage IA disease simply because the tumor is confined to the endometrium. The positive peritoneal washings mandate upstaging to stage IIIA and require adjuvant radiotherapy, not observation alone 1, 2. Treating as stage IA would result in undertreatment and increased risk of recurrence.