Oncology · Module 4 of 4

Checkpoint Inhibitors and Hormonal Oncology

Mechanisms, irAE management, biomarkers, and CAR-T toxicity

CTLA-4 inhibitors (ipilimumab) act at the T-cell priming stage in lymph nodes, blocking the B7-CTLA-4 interaction that normally attenuates T-cell activation and depleting regulatory T cells via ADCC. This broad immune amplification across many T-cell clones generates a wider and more severe immune-related adverse event (irAE) spectrum than PD-1/PD-L1 inhibitors, which act more locally in the tumor microenvironment. All checkpoint inhibitors are large-molecule biologics with no CYP metabolism and no hepatic or renal dose adjustment requirements.
irAE management follows a grade-based algorithm: grade 2 toxicities generally warrant holding the ICI and starting prednisone 1 mg/kg/day; grade 3–4 toxicities require IV methylprednisolone. Steroids must be tapered slowly over at least 4–6 weeks — premature taper reliably causes relapse. The steroid-refractory agent differs critically by organ: colitis uses infliximab (anti-TNF), but immune hepatitis must never receive infliximab (which is itself hepatotoxic) — mycophenolate mofetil is the correct second-line agent. Adrenal crisis from ICI-induced hypophysitis or adrenalitis requires immediate IV hydrocortisone without waiting for laboratory confirmation.
ICI predictive biomarkers operate across two axes: tumor-specific (PD-L1 TPS and CPS, TMB, dMMR/MSI-H) and histology-agnostic. Pembrolizumab has tumor-agnostic approvals for both TMB-high (≥10 mutations/megabase) and dMMR/MSI-H solid tumors, making universal MSI testing of all solid tumors a standard recommendation. PD-L1 TPS (tumor proportion score) quantifies staining on tumor cells; CPS (combined positive score) includes tumor and immune cells — the applicable score depends on tumor type and ICI indication.
Hormonal therapy carries four high-stakes drug interactions. Enzalutamide is a potent CYP3A4 inducer that dramatically reduces levels of anticoagulants, docetaxel, and most co-administered oncology drugs — full medication review is mandatory before starting and after any dose change. Tamoxifen converted to its active metabolite endoxifen by CYP2D6 — paroxetine and fluoxetine reduce this conversion by 65–75%; substitute venlafaxine. Abiraterone requires prednisone to suppress ACTH-driven mineralocorticoid excess and must be taken on an empty stomach. GnRH agonist initiation with high-burden skeletal metastases requires 4 weeks of antiandrogen cover to prevent the testosterone flare from precipitating cord compression.
CAR-T cell toxicity takes two distinct forms requiring opposite treatments. Cytokine release syndrome (CRS) — fever, hypotension, hypoxia from massive IL-6 release — responds to tocilizumab (anti-IL-6 receptor) as first-line, with dexamethasone added for severe or refractory cases. Immune effector cell-associated neurotoxicity syndrome (ICANS) — confusion, aphasia, tremor, seizure — is treated with dexamethasone only; tocilizumab is ineffective for ICANS and may worsen CNS toxicity by increasing CNS cytokine accumulation. Never give tocilizumab for ICANS.

ADT = androgen deprivation therapy · AI = aromatase inhibitor · AR = androgen receptor · CAR-T = chimeric antigen receptor T cell · CPS = combined positive score · CRS = cytokine release syndrome · CTLA-4 = cytotoxic T-lymphocyte antigen 4 · CYP = cytochrome P450 · dMMR = mismatch repair deficiency · GnRH = gonadotropin-releasing hormone · ICI = immune checkpoint inhibitor · ICANS = immune effector cell-associated neurotoxicity syndrome · IL-6 = interleukin-6 · irAE = immune-related adverse event · MSI-H = microsatellite instability-high · PD-1 = programmed death 1 · PD-L1 = programmed death ligand 1 · SERM = selective estrogen receptor modulator · TMB = tumor mutational burden · TPS = tumor proportion score · Treg = regulatory T cell

Checkpoint Inhibitor Biology — CTLA-4 vs PD-1/PD-L1

CTLA-4 Inhibition

Ipilimumab — Priming Stage

Site of action: T-cell priming in lymph nodes (not the tumor)
Mechanism: blocks CTLA-4/B7 interaction → removes the brake on T-cell co-stimulation; also depletes regulatory T cells via ADCC (IgG1 Fc)
Effect: broad amplification across many T-cell clones → wider irAE spectrum than PD-1/PD-L1 agents
Combination with nivolumab (PD-1): synergistic anti-tumor activity; significantly higher irAE rate — used in melanoma, RCC, NSCLC, MSI-H colorectal cancer

PD-1 / PD-L1 Inhibition

Nivolumab, Pembrolizumab, Atezolizumab & Others

Site of action: effector phase in tumor microenvironment — restores T-cell killing of PD-L1-expressing tumor cells
PD-1 inhibitors (IgG4): nivolumab, pembrolizumab, cemiplimab
PD-L1 inhibitors: atezolizumab, durvalumab, avelumab
More tumor-localized immune activation → narrower irAE spectrum than CTLA-4 inhibition
No CYP metabolism; no hepatic or renal dose adjustment; half-life 2–4 weeks

irAE Management by Organ

Organ	Grade 2	Grade 3–4	Steroid-Refractory Agent	Permanent Discontinuation?
Colitis	Hold ICI; prednisone 1 mg/kg/day orally; monitor for perforation	Hospital admission; IV methylprednisolone 1–2 mg/kg/day	Infliximab (anti-TNF) 5 mg/kg IV	Grade 4 colitis: yes
Hepatitis	Hold ICI; prednisone 0.5–1 mg/kg/day; LFTs every 1–2 weeks	IV methylprednisolone; liver biopsy if diagnosis uncertain	Mycophenolate mofetil — NEVER infliximab (hepatotoxic)	Grade 3+: likely permanent
Pneumonitis	Hold ICI; prednisone 1–2 mg/kg/day; bronchoscopy to exclude infection	IV methylprednisolone; CT chest; consider bronchoscopy with BAL	Mycophenolate mofetil or IVIG	Grade 3–4: yes
Endocrine (thyroid, pituitary, adrenal)	Continue ICI; initiate hormone replacement (levothyroxine, hydrocortisone)	Acute adrenal crisis: IV hydrocortisone 100 mg immediately — do not wait for labs	N/A — steroids do not restore gland function; replacement is permanent	Usually no — continue ICI with lifelong hormone replacement

Predictive Biomarkers & Hormonal Therapy Interactions

ICI Predictive Biomarkers

PD-L1, TMB, dMMR/MSI-H

PD-L1 TPS (tumor proportion score): staining on tumor cells only — used in NSCLC (pembrolizumab monotherapy: TPS ≥50%; combination therapy: TPS ≥1%)
PD-L1 CPS (combined positive score): tumor + immune + stromal cells — used in gastric, head and neck, urothelial, cervical cancers
TMB-high (≥10 mutations/megabase): tumor-agnostic pembrolizumab approval (KEYNOTE-158)
dMMR/MSI-H: tumor-agnostic pembrolizumab approval; most prevalent in colorectal and endometrial cancers; universal MSI testing of all solid tumors recommended

Hormonal Therapy Drug Interactions

Four High-Stakes Interactions

Enzalutamide: potent CYP3A4 inducer — reduces warfarin, DOACs, docetaxel, and most co-administered drugs; full medication review mandatory before starting and after dose changes
Tamoxifen + paroxetine/fluoxetine: CYP2D6 inhibition reduces endoxifen by 65–75% → substitute venlafaxine or gabapentin for hot flash management
Abiraterone: prednisone co-administration mandatory (suppresses ACTH-driven mineralocorticoid excess → prevents hypertension, hypokalemia, edema); take on empty stomach (high-fat food increases exposure 10-fold)
GnRH agonist + bulky skeletal metastases: antiandrogen (bicalutamide) 4 weeks before and during GnRH agonist initiation — prevents testosterone flare that can precipitate spinal cord compression or urinary obstruction

CAR-T Cell Toxicity — CRS vs ICANS

CRS — Cytokine Release Syndrome

IL-6-Mediated Systemic Toxicity

Mechanism: massive IL-6 release as CAR-T cells lyse tumor → systemic inflammatory response
Hallmark: fever (required for CRS diagnosis); severity defined by hypotension and hypoxia grade
Biomarkers: markedly elevated ferritin, CRP, IL-6 levels correlate with severity
Treatment: tocilizumab (anti-IL-6 receptor) first-line for grade 2+; add dexamethasone for grade 3–4 or tocilizumab-refractory CRS
Supportive care: vasopressors for refractory hypotension; supplemental O₂ or mechanical ventilation for hypoxia

ICANS — Neurotoxicity Syndrome

CNS Immune Effector Toxicity

Mechanism: CNS CAR-T trafficking, blood-brain barrier disruption, and direct cytokine-mediated CNS injury
Presentation: confusion and disorientation (early), aphasia, tremor, writing impairment, seizures, cerebral edema (severe)
Grading: ICE score (Immune Effector Cell Encephalopathy) — orientation, naming, commands, writing, attention
Treatment: dexamethasone — the only effective agent for ICANS
Tocilizumab is NOT effective for ICANS and may worsen CNS toxicity — do not use
Levetiracetam seizure prophylaxis for grade 2+ ICANS

Non-Negotiable Clinical Rules

Seven Rules for This Module

irAE steroid taper must be slow — at least 4–6 weeks minimum; premature taper reliably causes irAE relapse. For steroid-refractory irAEs, the second-line agent is organ-specific: colitis → infliximab; hepatitis → mycophenolate mofetil (infliximab is hepatotoxic and is absolutely contraindicated in immune hepatitis). Adrenal crisis from ICI-induced adrenalitis or hypophysitis: IV hydrocortisone 100 mg immediately — do not wait for lab results; delay risks cardiovascular collapse. All endocrine irAEs require lifelong hormone replacement; the ICI can usually be continued.

For CAR-T toxicity: CRS → tocilizumab (anti-IL-6 receptor); ICANS → dexamethasone only. Tocilizumab must not be given for ICANS — it does not cross the blood-brain barrier to neutralize CNS cytokines and may paradoxically worsen CNS inflammation by shunting IL-6 centrally. Treat CRS and ICANS as distinct entities requiring distinct management even when they occur simultaneously.

Chapter Complete · Anti-Cancer Drugs Part 2 · End of Pharmacology Infographic Series

Four Modules — Targeted and Immunological Oncology

This chapter completed the oncology pharmacology sequence with the targeted and biological agents that have redefined cancer treatment over the past two decades. Module 1 traced the kinase inhibitor generations for BCR-ABL, EGFR, and ALK/ROS1 — establishing how mutation testing drives generation selection and how gatekeeper mutations (T315I, T790M) mandate generation escalation. Module 2 surveyed the breadth of small molecule inhibitors — BRAF/MEK, CDK4/6, BCL-2, PARP, FLT3, IDH, BTK, PI3K, mTOR, proteasome inhibitors, and IMiDs — organized by their clinical emergencies, companion diagnostic requirements, and mandatory prophylaxis rules. Module 3 covered monoclonal antibodies and antibody-drug conjugates, distinguishing their pharmacokinetics from small molecules and establishing the non-negotiable clinical rules around trastuzumab cardiotoxicity, bevacizumab surgical timing, daratumumab blood bank notification, rituximab HBV screening, and T-DXd ILD monitoring. Module 4 closed the series with immune checkpoint inhibitor biology, irAE organ-based management, predictive biomarkers, hormonal therapy drug interactions, and the critical CRS-versus-ICANS treatment distinction in CAR-T therapy.

Across both oncology chapters, the unifying discipline is systematic thinking before every prescription: confirm the molecular target, check the companion diagnostic, know the class-defining toxicity and its management, verify the mandatory prophylaxis, and identify the one drug interaction that can be fatal. Pharmacology does not end with mechanism — it ends with the patient safely receiving the right drug at the right dose with the right monitoring in place.

References

Author / Source	Title	Publication
Katzung BG (ed)	Basic & Clinical Pharmacology, 15th ed.	McGraw-Hill, 2021
Brunton LL, Knollmann BC (eds)	Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed.	McGraw-Hill, 2023
Larkin J, Chiarion-Sileni V, Gonzalez R, et al	Five-year survival with combined nivolumab and ipilimumab in advanced melanoma	N Engl J Med. 2019;381(16):1535–1546
Herbst RS, Baas P, Kim DW, et al	Pembrolizumab versus docetaxel for previously treated, PD-L1-positive, advanced non-small-cell lung cancer (KEYNOTE-010)	Lancet. 2016;387(10027):1540–1550
Haanen J, Obeid M, Spain L, et al	Management of toxicities from immunotherapy: ESMO clinical practice guideline	Ann Oncol. 2022;33(12):1217–1238
Delivanis DA, Gustafson MP, Bornschlegl S, et al	Pembrolizumab-induced thyroiditis: comprehensive clinical review	J Clin Endocrinol Metab. 2017;102(8):2770–2780
Marabelle A, Fakih M, Lopez J, et al	Association of tumour mutational burden with outcomes in patients with advanced solid tumours treated with pembrolizumab (KEYNOTE-158)	Lancet Oncol. 2020;21(10):1353–1365
Le DT, Durham JN, Smith KN, et al	Mismatch repair deficiency predicts response of solid tumors to PD-1 blockade	Science. 2017;357(6349):409–413
Davis ID, Martin AJ, Stockler MR, et al	Enzalutamide with standard first-line therapy in metastatic prostate cancer	N Engl J Med. 2019;381(2):121–131
Davies C, Pan H, Godwin J, et al	Long-term effects of continuing adjuvant tamoxifen to 10 years versus stopping at 5 years (ATLAS)	Lancet. 2013;381(9869):805–816
Maude SL, Laetsch TW, Buechner J, et al	Tisagenlecleucel in children and young adults with B-cell lymphoblastic leukemia	N Engl J Med. 2018;378(5):439–448
Strosberg J, El-Haddad G, Wolin E, et al	Phase 3 trial of 177Lu-dotatate for midgut neuroendocrine tumors	N Engl J Med. 2017;376(2):125–135
Antonia SJ, Villegas A, Daniel D, et al	Overall survival with durvalumab after chemoradiotherapy in stage III NSCLC	N Engl J Med. 2018;379(24):2342–2350
Neelapu SS, Locke FL, Bartlett NL, et al	Axicabtagene ciloleucel CAR T-cell therapy in refractory large B-cell lymphoma	N Engl J Med. 2017;377(26):2531–2544
Reck M, Rodriguez-Abreu D, Robinson AG, et al	Pembrolizumab versus chemotherapy for PD-L1-positive non-small-cell lung cancer	N Engl J Med. 2016;375(19):1823–1833