Is pembrolizumab (Keytruda) safe to give when a patient has a markedly elevated morning serum cortisol of about 75 µg/dL?

Do Not Give Pembrolizumab with Morning Cortisol of 75 µg/dL

A morning cortisol of 75 µg/dL (approximately 2070 nmol/L) is markedly elevated and suggests either severe physiologic stress, exogenous Cushing syndrome, or endogenous hypercortisolism—pembrolizumab should be withheld until the underlying cause is identified and cortisol levels are controlled.

Why This Matters for Pembrolizumab Safety

Supraphysiologic cortisol levels create a profoundly immunosuppressive environment that directly contradicts the mechanism of action of pembrolizumab, which relies on activating T-cell immunity. More critically, elevated cortisol can mask immune-related adverse events (irAEs) and severe organ toxicity that would otherwise present with recognizable symptoms 1.

The Evidence Against Using Pembrolizumab in Hypercortisolism

A case report documented rapid disease progression and fatal liver failure in a patient with cortisol-secreting adrenocortical carcinoma treated with pembrolizumab 1. The supraphysiological cortisol levels likely rendered the immunotherapy ineffective while simultaneously masking pembrolizumab-induced hepatotoxicity—the patient developed transaminitis that was initially transient, but ultimately progressed to fulminant liver failure. The immunosuppressive effects of excess cortisol prevented both therapeutic efficacy and early recognition of life-threatening drug toxicity 1.

Clinical Algorithm for This Scenario

Step 1: Confirm the Cortisol Level

• Normal morning cortisol: 5-25 µg/dL (138-690 nmol/L)
• Your patient's level of 75 µg/dL is 3-15 times the upper limit of normal
• Repeat the test to exclude laboratory error
• Check if the patient is on exogenous corticosteroids (including inhaled, topical, or intra-articular formulations within 2 months) 2

Step 2: Identify the Source of Hypercortisolism

• Measure ACTH simultaneously with morning cortisol 3
  • Low/suppressed ACTH → adrenal source (adenoma, carcinoma, or exogenous steroids)
  • Elevated ACTH → pituitary or ectopic source
• Obtain 24-hour urinary free cortisol to confirm Cushing syndrome 3
• Imaging (CT/MRI) of adrenals and pituitary as indicated

Step 3: Hold Pembrolizumab Until Resolution

• Do not administer pembrolizumab until cortisol normalizes
• If the patient has exogenous Cushing syndrome from therapeutic steroids, taper to physiologic doses (equivalent to prednisone 4-6 mg daily or hydrocortisone 15-25 mg daily) 2
• If endogenous Cushing syndrome, treat the underlying cause (surgical resection, medical management with ketoconazole or mitotane) 3

Step 4: When Can Pembrolizumab Be Safely Resumed?

• Morning cortisol should be <10 µg/dL (276 nmol/L) before considering immunotherapy 2
• Ideally, cortisol should normalize to the reference range (5-25 µg/dL)
• If the patient was on supraphysiologic steroids, ensure they are on physiologic replacement doses only and confirm HPA axis recovery with morning cortisol >10 µg/dL (300 nmol/L) 2

Critical Pitfalls to Avoid

Pitfall 1: Assuming the Patient Can Tolerate Pembrolizumab Despite High Cortisol

The immunosuppressive effects of hypercortisolism will likely render pembrolizumab ineffective while increasing infection risk and masking irAEs 1. This is not a theoretical concern—it has resulted in patient death 1.

Pitfall 2: Missing Exogenous Steroid Exposure

Patients may not volunteer information about:

• High-dose inhaled corticosteroids (>1 year use) 2
• Topical steroids in large quantities
• Intra-articular injections within the past 2 months 2
• Multiple simultaneous glucocorticoid formulations 2
• Medications that inhibit cytochrome P450 3A4, which can increase steroid exposure 2

Pitfall 3: Not Recognizing That Pembrolizumab Can Cause Adrenal Insufficiency

While your patient has the opposite problem (hypercortisolism), it's worth noting that pembrolizumab commonly causes hypophysitis with secondary adrenal insufficiency 4, 5, 6, 7. The FDA label for pembrolizumab specifically warns about hypothyroidism (12-14% incidence) and other endocrinopathies 8. If this patient eventually receives pembrolizumab after cortisol normalization, they will need:

• Baseline morning cortisol, ACTH, TSH, and free T4 before each cycle 4
• Clinical monitoring for fatigue, hypotension, hyponatremia, nausea 4, 5, 6, 7
• Immediate cortisol replacement if adrenal insufficiency develops, as thyroid replacement before cortisol replacement can precipitate adrenal crisis 4

Practical Considerations

If the patient has cancer requiring urgent treatment, consider alternative chemotherapy regimens that do not rely on immune activation. Pembrolizumab will not work effectively in the setting of severe hypercortisolism, and delaying to correct the cortisol excess is the only rational approach 1.

If the cortisol elevation is from therapeutic steroids, work with the prescribing physician to taper to the lowest effective dose. According to guidelines, patients on supraphysiologic glucocorticoids should not be tested for adrenal insufficiency or considered for immunotherapy until they reach physiologic replacement doses 2.

Document the decision clearly in the medical record, including the specific cortisol value, the rationale for holding pembrolizumab, and the plan for reassessment. This protects both the patient and the treatment team.