Managing Refractory Diarrhea in Metastatic Breast Cancer

Refractory Diarrhea in Metastatic Breast Cancer

Case Presentation: Diagnostic Dilemmas Post-Chemotherapy & Immunotherapy

Presented for Oncology Ward Review

Patient Profile & Admission

• Middle-aged female • Diagnosis: Metastatic Breast Cancer

• Recent Chemotherapy (Day 10 post-cycle) • Current Immunotherapy: Pembrolizumab

• Presented with: Nausea, vomiting, abdominal pain • Chief Complaint: Non-bloody loose stools

Initial Clinical Assessment

• Tachycardia on arrival • Other observations stable • ECG: Fast Atrial Fibrillation (AF)

• CRP > 400 mg/L (Severe Inflammation) • Hypokalemia (Low K+) • Hypomagnesemia (Low Mg+) • AKI Stage 2

Phase 1: Initial Management & Response

• IV Fluids (Resuscitation) • IV Electrolyte Replacement (Mg, K) • IV Ceftazidime (Empiric coverage)

✓ AKI Resolved ✓ Fast AF Resolved ✓ Inflammatory markers (CRP) improving

⚠ Diarrhea persisted ⚠ No improvement in stool frequency

Diagnostic Dilemma: Interpretation of Stool Analysis

PCR Positive (+) Toxin Negative (-)

• Indicates presence of C. diff organism (colonization potential). • Absence of free toxin suggests it may not be the primary driver of current symptoms. • HOWEVER: Patient is immunocompromised (Chemo + Pembrolizumab) with active colitis symptoms.

Decided to treat as active C. diff infection due to high clinical suspicion and host vulnerability.

Refractory Course: Escalation and Failure

1. Started Oral Vancomycin (Standard dose) 2. Escalated to Fidaxomicin + IV Metronidazole (Dual therapy) 3. Duration: Multiple days on dual therapy

Result: No improvement. Frequency increased to 18-22 episodes/day.

Endoscopic Investigation

• Procedure: Flexible Sigmoidoscopy • Visual Finding: Pseudomembranous Colitis • Action: Biopsies taken for histology & CMV IHC

Classic appearance of C. Difficile infection (yellow-white plaques). However, the patient failed maximal medical therapy for C. Diff, raising suspicion of alternative or co-pathology.

Differential 2: Pembrolizumab-Induced Colitis

• Mechanism: Immune Checkpoint Inhibitor (PD-1 blockade) unleashes T-cells, causing autoimmune-like damage to normal mucosa. • Prevalence: Colitis occurs in 2-5% of patients.

• Timing: Can occur anytime (often weeks after initiation). • Symptoms: Refractory diarrhea, abdominal pain (matches patient). • Endoscopy: Usually ulceration/inflammation, but pseudomembranes are NOT typical (though superinfection possible).

Differential 3: CMV Colitis

• Serology: IgM Weakly Positive • Significance: Suggests recent infection or reactivation (common in immunocompromised).

• Pending: CMV Nucleic Acid Detection (PCR) - Viral Load. • Pending: Biopsy Immunohistochemistry (Gold Standard).

Current Management Strategy

• STOPPED: Fidaxomicin and IV Metronidazole (Treatment Failure) • STARTED: High-Dose Oral Vancomycin (250mg every 4 hours)

• Proposed: Fecal Microbiota Transplant (FMT) • Status: Microbiology review awaited to determine suitability.

Summary & Key Takeaways

1. Complexity: Refractory diarrhea in oncology is often multifactorial (Infection vs. Toxicity).

2. Diagnostics: C. Diff PCR positive / Toxin negative presents a stewardship challenge, but immunocompromised status validates aggressive treatment.

3. Differentials: Always consider IO-Colitis (Pembrolizumab) and CMV reactivation when initial therapies fail.