# Clinical Cases: Tumor Immunology

## Case 1: Metastatic Melanoma Treated with Checkpoint Inhibitors

### Patient Presentation
**Demographics:** 58-year-old male

**Chief Complaint:** Follow-up for metastatic melanoma treatment

**History of Present Illness:**
The patient was diagnosed with BRAF wild-type metastatic melanoma 3 months ago with lung and liver metastases. He was started on combination checkpoint inhibitor therapy with ipilimumab (anti-CTLA-4) and nivolumab (anti-PD-1). After 4 cycles, imaging shows significant tumor regression, but he now presents with new symptoms of fatigue, diarrhea (6-8 watery stools/day), and skin rash.

**Past Medical History:**
- Melanoma diagnosed 3 months ago (BRAF wild-type)
- Hypertension
- No autoimmune disease history

**Medications:**
- Ipilimumab/nivolumab combination (4 cycles completed)
- Lisinopril 10 mg daily

**Physical Examination:**
- Blood pressure: 102/68 mmHg (lower than baseline)
- Heart rate: 92 bpm
- Temperature: 37.1C
- General: Fatigued appearance
- Skin: Diffuse maculopapular rash on trunk and extremities
- Abdomen: Mild diffuse tenderness, hyperactive bowel sounds
- Thyroid: Normal size

### Workup and Results

**Laboratory Studies:**
- WBC: 8,200/mcL (normal)
- Hemoglobin: 12.8 g/dL
- TSH: 12.4 mU/L (elevated)
- Free T4: 0.6 ng/dL (low)
- Cortisol (AM): 4.2 mcg/dL (low-normal)
- CRP: 45 mg/L (elevated)
- Stool studies: Negative for infection

**Imaging:**
- CT chest/abdomen: 60% reduction in tumor burden compared to baseline

**Colonoscopy:**
- Diffuse colonic inflammation with ulceration
- Biopsy: Lymphocytic infiltration consistent with immune-mediated colitis

### Clinical Image

![Immune Checkpoint Inhibitor Colitis](case_01_image.jpg)

*Colonoscopy demonstrating immune-related colitis with diffuse inflammation, ulceration, and erythema. Histology shows lymphocytic infiltration of the colonic mucosa, characteristic of checkpoint inhibitor-induced colitis.*

### Diagnosis
**Immune-Related Adverse Events (irAEs) from Checkpoint Inhibitor Therapy:**
1. Grade 3 immune-mediated colitis
2. Checkpoint inhibitor-induced hypothyroidism
3. Grade 2 cutaneous irAE (rash)

### Discussion
This case illustrates checkpoint inhibitor toxicity:

- **Mechanism of irAEs**: The lecture explains that irAEs result from autoimmune inflammation in normal tissues. By releasing the "brakes" on T cells (blocking CTLA-4 and PD-1), checkpoint inhibitors enhance anti-tumor immunity but also permit autoreactivity.

- **Combination Therapy Toxicity**: The lecture notes that combining anti-CTLA-4 and anti-PD-1 increases efficacy but also toxicity. These agents work through different mechanisms: ipilimumab enhances T cell priming, while nivolumab reinvigorates exhausted T cells.

- **Common irAE Sites**: The lecture identifies skin, GI tract, liver, and endocrine glands as most commonly affected organs. This patient demonstrates colitis, thyroiditis, and dermatitis.

- **Endocrine irAEs**: Thyroiditis from checkpoint inhibitors often progresses to permanent hypothyroidism requiring lifelong replacement. Primary adrenal insufficiency and hypophysitis can also occur.

### Treatment Plan
1. **Colitis Management (Grade 3):**
   - Hold checkpoint inhibitors
   - High-dose corticosteroids (methylprednisolone 1-2 mg/kg/day)
   - If no improvement in 3 days: add infliximab (anti-TNF)
   - Supportive care: IV fluids, electrolyte replacement

2. **Hypothyroidism:**
   - Levothyroxine replacement (permanent treatment likely needed)
   - Does not require holding immunotherapy

3. **Rash (Grade 2):**
   - Topical corticosteroids
   - Oral antihistamines

4. **Monitoring:**
   - Daily clinical assessment
   - Repeat TSH in 6 weeks
   - Morning cortisol to rule out adrenal insufficiency

5. **Future Immunotherapy:**
   - May resume anti-PD-1 monotherapy after colitis resolves
   - Avoid ipilimumab (higher colitis risk)

### Teaching Points
1. irAEs result from T cell activation against normal tissues
2. Combination checkpoint inhibitors increase efficacy and toxicity
3. Grade 3-4 irAEs require high-dose corticosteroids
4. Endocrine irAEs (thyroiditis) may require lifelong hormone replacement
5. Tocilizumab (anti-IL-6) treats CRS; corticosteroids treat most irAEs

---

## Case 2: CAR-T Cell Therapy with Cytokine Release Syndrome

### Patient Presentation
**Demographics:** 34-year-old male

**Chief Complaint:** Fever and confusion 5 days after CAR-T infusion

**History of Present Illness:**
The patient has relapsed/refractory diffuse large B-cell lymphoma (DLBCL) after 3 prior lines of therapy. He received axicabtagene ciloleucel (CD19-targeted CAR-T cells) 5 days ago. He developed fever (39.5C) on day 3 post-infusion with progressive hypotension, now requiring vasopressors. Today he is confused and disoriented.

**Past Medical History:**
- DLBCL diagnosed 2 years ago
- Relapsed after R-CHOP, salvage chemotherapy, and autologous transplant
- No other significant medical history

**Physical Examination:**
- Blood pressure: 82/50 mmHg (on norepinephrine)
- Heart rate: 118 bpm
- Temperature: 40.1C
- Oxygen saturation: 92% on 4L nasal cannula
- General: Ill-appearing, confused
- Lungs: Bibasilar crackles
- Neurologic: Oriented only to self, mild tremor

### Workup and Results

**Laboratory Studies:**
- WBC: 1,200/mcL (pancytopenic from lymphodepletion)
- Hemoglobin: 8.4 g/dL
- Platelets: 42,000/mcL
- Ferritin: 18,500 ng/mL (markedly elevated)
- CRP: 285 mg/L (markedly elevated)
- IL-6: 2,840 pg/mL (markedly elevated)
- Fibrinogen: 98 mg/dL (low - DIC concern)
- LDH: 1,250 U/L

**Imaging:**
- CT head: No acute abnormality
- Chest X-ray: Bilateral pulmonary infiltrates

### Clinical Image

![CRS Pathophysiology](case_01_image.jpg)

*Diagram illustrating cytokine release syndrome (CRS) pathophysiology following CAR-T cell activation. Massive cytokine release, particularly IL-6, leads to systemic inflammatory response with fever, hypotension, capillary leak, and multi-organ dysfunction.*

### Diagnosis
**Grade 4 Cytokine Release Syndrome (CRS) with Immune Effector Cell-Associated Neurotoxicity Syndrome (ICANS)**

CRS Grade 4 criteria met:
- Fever >38C
- Hypotension requiring vasopressors
- Hypoxia requiring supplemental oxygen

ICANS features:
- Confusion/encephalopathy

### Discussion
This case demonstrates CAR-T complications:

- **CRS Mechanism**: The lecture describes how CRS results from massive cytokine production when activated CAR-T cells encounter target antigen. IL-6 is the key driver, produced by monocytes/macrophages activated by CAR-T cells.

- **IL-6 as Key Cytokine**: The lecture identifies IL-6 as the key cytokine in CRS pathophysiology. Elevated ferritin and CRP are characteristic markers.

- **ICANS**: The lecture explains that ICANS (neurotoxicity) presents with confusion, tremor, word-finding difficulty, and can progress to seizures. It may occur with or after CRS.

- **Tocilizumab First-Line**: The lecture states that tocilizumab (anti-IL-6 receptor) is first-line for CRS because it rapidly reverses cytokine-mediated inflammation without impairing CAR-T cell efficacy against tumor.

### Treatment Plan
1. **CRS Treatment:**
   - Tocilizumab 8 mg/kg IV (can repeat in 8 hours if needed)
   - Continue vasopressors
   - Supportive care: IV fluids, oxygen

2. **ICANS Treatment:**
   - Dexamethasone 10 mg IV every 6 hours
   - Corticosteroids are preferred for neurotoxicity (tocilizumab doesn't cross BBB well)
   - Seizure prophylaxis (levetiracetam)

3. **Monitoring:**
   - ICU level care
   - Serial neurologic assessments
   - Daily CRP, ferritin, IL-6

4. **Supportive Care:**
   - Blood product support as needed
   - Broad-spectrum antibiotics (infectious workup, though CRS most likely)

5. **Expected Course:**
   - Most CRS resolves within 1-2 weeks
   - Response assessment at day 28-30

### Teaching Points
1. CRS is driven by massive cytokine release, particularly IL-6
2. Tocilizumab (anti-IL-6R) is first-line for CRS
3. ICANS is treated with corticosteroids (tocilizumab less effective)
4. Elevated ferritin and CRP are characteristic CRS markers
5. B-cell aplasia is an expected "on-target, off-tumor" effect of CD19 CAR-T

---

## Case 3: MSI-High Colorectal Cancer Responding to Immunotherapy

### Patient Presentation
**Demographics:** 52-year-old female

**Chief Complaint:** Follow-up for metastatic colorectal cancer treatment

**History of Present Illness:**
The patient was diagnosed with metastatic colorectal cancer 6 months ago. Molecular testing revealed the tumor is microsatellite instability-high (MSI-H) with deficient mismatch repair (dMMR). She was started on pembrolizumab (anti-PD-1) as first-line therapy. After 4 cycles, she reports feeling well with improved energy and appetite.

**Past Medical History:**
- Colorectal cancer with liver metastases
- No family history of Lynch syndrome
- No prior chemotherapy

**Physical Examination:**
- General: Well-appearing, improved from prior visits
- Abdomen: Soft, non-tender, no hepatomegaly
- No lymphadenopathy

### Workup and Results

**Laboratory Studies:**
- CEA: 12 ng/mL (down from 156 ng/mL at diagnosis)
- LFTs: Normal
- CBC: Normal

**Imaging:**
- CT chest/abdomen/pelvis: 70% reduction in liver metastases

**Molecular Testing (at diagnosis):**
- MSI-H (microsatellite instability-high)
- dMMR (deficient mismatch repair: MLH1 loss)
- Tumor mutational burden: 42 mutations/Mb (high)

### Clinical Image

![MSI-H Tumor Response](case_01_image.jpg)

*CT comparison showing significant tumor regression in MSI-H colorectal cancer liver metastases after pembrolizumab treatment, demonstrating the excellent response of high tumor mutational burden tumors to checkpoint inhibitor therapy.*

### Diagnosis
**MSI-High Metastatic Colorectal Cancer with Excellent Response to Checkpoint Inhibitor**

### Discussion
This case illustrates predictors of immunotherapy response:

- **MSI-H/dMMR Predicts Response**: The lecture describes how MSI-H tumors have deficient mismatch repair, leading to accumulation of mutations and high tumor mutational burden (TMB). This generates numerous neoantigens that make tumors highly immunogenic.

- **TMB Correlates with Response**: The lecture notes that tumor mutational burden correlates with neoantigen load and checkpoint inhibitor response. MSI-H colorectal cancers have 10-100x higher TMB than microsatellite stable tumors.

- **Tissue-Agnostic Approval**: The lecture explains that pembrolizumab has tissue-agnostic FDA approval for MSI-H/dMMR tumors regardless of site of origin - the first such approval based on a biomarker rather than tumor type.

- **"Hot" vs "Cold" Tumors**: MSI-H tumors are typically "hot" (T-cell infiltrated) due to their high neoantigen load, making them excellent candidates for checkpoint inhibitors.

### Treatment Plan
1. **Continue Pembrolizumab:**
   - Standard dosing every 3 weeks
   - Continue for up to 2 years if responding

2. **Monitoring:**
   - CEA every 6 weeks
   - CT imaging every 3 months
   - Monitor for irAEs

3. **Genetic Counseling:**
   - Consider Lynch syndrome evaluation
   - MLH1 promoter methylation testing (sporadic vs germline)
   - Family history assessment

4. **Future Considerations:**
   - If complete response: consider treatment discontinuation at 2 years
   - Surveillance protocol after completion

### Teaching Points
1. MSI-H/dMMR tumors have high TMB and are highly responsive to checkpoint inhibitors
2. Pembrolizumab has tissue-agnostic approval for MSI-H/dMMR tumors
3. Hot tumors (T-cell infiltrated) respond better to immunotherapy than cold tumors
4. Testing for MSI/MMR status should be routine in colorectal cancer
5. Lynch syndrome should be considered in patients with dMMR tumors

---

## Image Reference

For visual reference of tumor immunology concepts, see:
- Radiopaedia: [Immunotherapy](https://radiopaedia.org/articles/immunotherapy-for-cancer) - Overview
- Wikipedia: [Checkpoint inhibitor](https://en.wikipedia.org/wiki/Checkpoint_inhibitor) - Mechanisms
- Radiopaedia: [CAR-T cell therapy](https://radiopaedia.org/articles/car-t-cell-therapy) - Complications

---

## Learning Points

1. **irAEs Mechanism**: Result from T cell activation against normal tissues when checkpoints are blocked

2. **CRS Treatment**: Tocilizumab (anti-IL-6R) is first-line; corticosteroids for ICANS

3. **MSI-H Predicts Response**: High tumor mutational burden generates neoantigens making tumors immunogenic

4. **Hot vs Cold Tumors**: Hot (T-cell infiltrated) tumors respond better to checkpoint inhibitors

5. **Tissue-Agnostic Approval**: Pembrolizumab approved for MSI-H/dMMR tumors regardless of site of origin