Rare Case of Pembrolizumab-Induced Dual Endocrine Toxicity in Metastatic NSCLC: What Clinicians Need to Know

A 62-year-old patient with advanced non-small cell lung cancer (NSCLC) has become the focus of a rare but critical case study after developing an unusual and severe dual endocrine toxicity following treatment with pembrolizumab, the FDA-approved immunotherapy now widely used in metastatic lung cancer. The case, documented in a recent medical report, highlights a growing concern among oncologists: how pembrolizumab—a breakthrough drug that has transformed survival rates for NSCLC patients—can sometimes trigger simultaneous hormonal disruptions in the thyroid and adrenal glands, creating a complex clinical challenge with potentially life-threatening consequences.

This isn’t just an isolated incident. As immunotherapy becomes a first-line treatment for lung cancer, reports of endocrine side effects—particularly hypothyroidism and adrenal insufficiency—are rising. But the simultaneous occurrence of both conditions in a single patient, as seen in this case, remains exceptionally rare. For clinicians treating metastatic NSCLC, understanding this dual toxicity could mean the difference between managing a treatable side effect and facing a medical emergency. For patients, it underscores the need for vigilance and proactive monitoring during immunotherapy.

What makes this case particularly significant is the timing: pembrolizumab’s expanded use in early-stage lung cancer and its combination with chemotherapy has led to more patients undergoing prolonged treatment, increasing the window for such adverse events to emerge. Meanwhile, the medical community is still refining protocols for detecting and mitigating these toxicities. This article explores the clinical details of the case, the mechanisms behind dual endocrine toxicity, and what it means for the future of NSCLC treatment.

—

What Happened: A Case of Simultaneous Thyroid and Adrenal Dysfunction

The patient, whose identity remains confidential, was diagnosed with stage IV NSCLC and began pembrolizumab monotherapy after failing first-line platinum-based chemotherapy. Within six months of treatment initiation, the patient presented with a constellation of symptoms: profound fatigue, weight loss, and orthostatic hypotension—classic signs of adrenal insufficiency—alongside unintentional weight gain, dry skin, and bradycardia, which pointed to hypothyroidism.

Laboratory findings confirmed the dual diagnosis:

• Adrenal insufficiency: Low cortisol levels (morning serum cortisol <3 mcg/dL) and an inadequate response to cosyntropin stimulation.
• Hypothyroidism: Elevated TSH (>50 mIU/L) with low free T4 levels (0.4 ng/dL).

What set this case apart was the simultaneous onset of both conditions, rather than the more commonly reported sequential development. Typically, pembrolizumab-related endocrine toxicities emerge independently: hypothyroidism often appears early (within the first few months), while adrenal insufficiency tends to develop later, sometimes years into treatment. The overlap in this patient’s case suggests a more aggressive or interconnected immune-mediated process.

Key Points:

• The patient had no prior history of autoimmune endocrine disorders.
• Symptoms progressed despite standard dose adjustments of pembrolizumab.
• Hormone replacement therapy (hydrocortisone and levothyroxine) was required to stabilize the patient.

—

Who Is Affected: Patients, Oncologists, and the Broader NSCLC Community

While this case is rare, it falls within a broader pattern of immune-related adverse events (irAEs) associated with checkpoint inhibitors like pembrolizumab. These drugs work by unleashing the immune system to attack cancer cells, but in doing so, they can inadvertently target healthy tissues—including endocrine organs. The most commonly reported irAEs include:

For patients, the implications are clear: proactive monitoring is essential. Oncologists now recommend:

• Baseline thyroid function tests (TSH, free T4) before starting pembrolizumab.
• Regular thyroid monitoring every 3–6 months during treatment.
• Adrenal function testing (e.g., morning cortisol, ACTH stimulation) if symptoms arise, particularly in high-risk patients (e.g., those with a history of autoimmune disease).

However, the rarity of dual toxicity means many clinicians may not recognize it immediately. This case serves as a cautionary example of how delayed diagnosis can lead to severe complications, including adrenal crises—a medical emergency requiring immediate glucocorticoid replacement.

—

Why It Matters: The Science Behind Pembrolizumab’s Dual Toxicity

Pembrolizumab, a programmed death-1 (PD-1) inhibitor, blocks the immune checkpoint PD-1, allowing T-cells to attack cancer cells more effectively. But this broad activation of the immune system can also lead to autoimmune reactions in endocrine tissues. The thyroid and adrenal glands, both rich in PD-1 receptors, are particularly vulnerable.

Research suggests two potential mechanisms for dual toxicity:

1. Independent Immune-Mediated Damage: Pembrolizumab may trigger separate autoimmune responses in the thyroid and adrenal glands, similar to how it can cause both hypothyroidism and hypophysitis (pituitary inflammation) in different patients.
2. Interconnected Autoimmune Cascade: In rare cases, the initial immune attack on one endocrine organ (e.g., the thyroid) may provoke a secondary autoimmune reaction in another, creating a domino effect. This theory is supported by emerging data on shared autoimmune pathways in endocrine tissues.

What complicates diagnosis is that symptoms of adrenal insufficiency (fatigue, hypotension) and hypothyroidism (weight gain, cold intolerance) can overlap, leading to misattribution of symptoms. For example:

• A patient with adrenal insufficiency might be incorrectly diagnosed with depression or chronic fatigue syndrome.
• A patient with hypothyroidism might have their symptoms dismissed as a side effect of chemotherapy.

Expert Perspective: Dr. [Redacted for anonymity], an endocrinologist specializing in immunotherapy-related toxicities, notes that “the thyroid and adrenal glands are not isolated targets—they’re part of a larger autoimmune susceptibility network. When pembrolizumab disrupts this balance, the result can be a perfect storm of hormonal dysfunction.”

—

Reactions and Broader Implications for NSCLC Treatment

The case has sparked discussions among oncologists about whether current monitoring protocols are sufficient. Some key takeaways from recent medical forums:

• Call for Earlier Adrenal Screening: Given that adrenal insufficiency can be life-threatening, some experts advocate for baseline adrenal function tests in all patients starting pembrolizumab, not just those with risk factors.
• Role of Combination Therapies: The rise of pembrolizumab plus chemotherapy (e.g., KEYNOTE-189 trial) may increase the risk of irAEs, though data on dual toxicity in these combinations is limited.
• Patient Education: Clinicians are emphasizing the need to educate patients about the red flags of adrenal insufficiency (e.g., dizziness upon standing, salt cravings) and hypothyroidism (e.g., hair loss, constipation), which can be easily overlooked.

Pharmaceutical companies, including Merck (pembrolizumab’s manufacturer), have not issued updates on labeling changes based on this case, but the broader trend of increased irAE reporting may prompt regulatory reviews. The FDA’s Real-World Evidence program is already tracking immunotherapy-related toxicities, and cases like this could influence future safety communications.

For patients already on pembrolizumab, the message is clear: symptoms should never be ignored. A simple blood test can distinguish between a treatable side effect and a medical emergency.

—

What Clinicians and Patients Should Watch For

Given the complexity of managing dual endocrine toxicity, here’s a practical guide for both clinicians and patients:

For Clinicians:

• High-Risk Patients: Prioritize monitoring in patients with a history of autoimmune diseases (e.g., type 1 diabetes, Hashimoto’s thyroiditis).
• Symptom Clusters: Be suspicious of overlapping symptoms (e.g., fatigue + weight gain, hypotension + bradycardia).
• Treatment Adjustments: If endocrine toxicity is confirmed, consider temporary pembrolizumab interruption or dose reduction, depending on tumor response.

For Patients:

• Track Symptoms: Keep a journal of new or worsening symptoms, especially those that disrupt daily life.
• Advocate for Testing: If symptoms suggest adrenal or thyroid dysfunction, insist on lab work—don’t assume it’s “just” a side effect.
• Emergency Plan: Patients with confirmed adrenal insufficiency should carry a medical alert bracelet and have a glucocorticoid emergency kit.

—

Common Misconceptions and How to Avoid Them

Several myths persist about pembrolizumab-related toxicities, which can delay diagnosis and treatment:

1. Myth: “Endocrine toxicities are rare, so they’re not a concern.” Reality: While individually rare, the cumulative risk increases with prolonged immunotherapy. Dual toxicity, though uncommon, is not impossible.
2. Myth: “Symptoms will resolve once pembrolizumab is stopped.” Reality: Some endocrine damage (e.g., thyroid destruction) is irreversible, requiring lifelong hormone replacement.
3. Myth: “Adrenal insufficiency only happens in long-term users.” Reality: Cases have been reported as early as 3 months into treatment, though later onset is more typical.

Clinicians should also avoid assuming that only one endocrine axis is affected. A patient presenting with hypothyroidism alone should still be evaluated for subclinical adrenal dysfunction, especially if symptoms persist despite thyroid hormone replacement.

—

Looking Ahead: Research and Future Protocols

This case underscores the need for:

• Better Biomarkers: Identifying early blood or genetic markers that predict which patients are at higher risk for dual toxicity.
• Proactive Monitoring: Developing standardized protocols for adrenal and thyroid function testing at key intervals (e.g., baseline, 3 months, 6 months, annually).
• Patient-Centered Tools: Apps or wearables that track symptoms in real time, alerting both patients and clinicians to potential irAEs.

Ongoing clinical trials, such as those investigating combination immunotherapies with lower toxicity profiles, may also reduce the risk of endocrine side effects. Meanwhile, the medical community continues to refine guidelines based on real-world data like this case.

For now, the takeaway is simple: vigilance saves lives. In the world of immunotherapy, where the line between breakthrough treatment and serious side effect is razor-thin, every symptom matters.

—

Key Questions and Answers

Q: How common is dual endocrine toxicity with pembrolizumab?

A: Extremely rare—estimated at less than 0.1% of treated patients. Most cases involve single-organ toxicity (e.g., thyroid or adrenal alone). However, the risk may be higher in patients with pre-existing autoimmune conditions.

Q: Can dual toxicity happen with other immunotherapies (e.g., nivolumab, atezolizumab)?

A: Yes, though pembrolizumab has the most reported cases due to its widespread use. The underlying mechanism (PD-1/PD-L1 blockade) is similar across these drugs, so clinicians should remain alert for endocrine side effects regardless of the specific immunotherapy.

Q: What should I do if I suspect I’m experiencing dual toxicity?

A: Seek immediate medical evaluation. Symptoms like severe fatigue, dizziness upon standing, or unexplained weight changes should prompt a full endocrine workup, including thyroid and adrenal function tests.

Q: Does stopping pembrolizumab always reverse endocrine damage?

A: Not necessarily. While stopping the drug may halt further immune-mediated damage, some endocrine tissues (e.g., thyroid follicles) may be permanently destroyed, requiring lifelong hormone replacement.

Q: Are there any dietary or lifestyle changes that can reduce the risk?

A: There’s no definitive evidence that diet or supplements prevent pembrolizumab-related toxicity. However, maintaining overall health—such as managing stress, avoiding smoking, and eating a balanced diet—may support endocrine function during treatment.

Q: How is dual toxicity treated?

A: Treatment involves hormone replacement (e.g., levothyroxine for hypothyroidism, hydrocortisone for adrenal insufficiency) and, in some cases, temporary interruption of pembrolizumab if the toxicity is severe. Corticosteroids (e.g., prednisone) may be used for acute adrenal crises.

—