Cetuximab & Panitumumab
Erbitux · Vectibix · Anti-EGFR antibody
TRPM6 magnesium wasting.
LYTE
MildOpen →
FGFR inhibitor
Pemigatinib
Pemazyre · Pemi
An FGFR1/2/3 inhibitor for cholangiocarcinoma — hyperphosphatemia is its near-universal class signature.
ModerateFGFR inhibitor · approved 2020
FGFR2-fusion/rearrangement cholangiocarcinoma
Signature kidney injury
Electrolyte Wasting
Representative incidence60%
Hyperphosphatemia is the most common adverse event in the pivotal FIGHT-202 trial, affecting roughly 60% of patients (any grade), with low rates of severe events; it is on-target and managed with monitoring, diet, and binders.
Source: Abou-Alfa et al., Lancet Oncol 2020
Mechanism of kidney injury
On-target FGFR1 inhibition disrupts FGF23-mediated suppression of proximal-tubular phosphate reabsorption (NaPi-2a/2c), increasing reabsorption and raising serum phosphate. Prolonged hyperphosphatemia with a high calcium-phosphate product risks nephrocalcinosis and ectopic/vascular calcification.
Clinical presentation
Asymptomatic hyperphosphatemia on routine monitoring; may co-occur with hypophosphatemia after dose interruption (a 'rebound') or hypocalcemia, and an elevated calcium-phosphate product. Soft-tissue mineralization risk if persistent; alopecia, dysgeusia, and nail changes are common non-renal effects.
Onset
Early — within the first cycles.
Reversibility
Reversible
Anticancer mechanism
Selective FGFR1/2/3 inhibitor blocking oncogenic FGFR signaling; approved for FGFR2-fusion/rearrangement-positive cholangiocarcinoma.
Management
Phosphate binders (e.g. sevelamer) and dietary restriction for phosphate >5.5 mg/dL; interrupt and dose-reduce for higher/persistent levels per label, and discontinue for persistent hyperphosphatemia despite optimal therapy. Monitor for nephrocalcinosis with prolonged elevation.
Risk factors
- Pre-existing CKD
- High calcium-phosphate product
- Concurrent vitamin D / phosphate intake
Prevention
- Routine phosphate monitoring
- Low-phosphate diet when phosphate rises
- Protocol-based dose modification (1-week-on schedule with planned breaks)
Note · Nephrocalcinosis is a theoretical/uncommon risk of sustained hyperphosphatemia; the dominant signal is reversible on-target hyperphosphatemia.
Clinical depth
Renal dose adjustment
No starting-dose change for mild-moderate renal impairment; severe impairment/dialysis not well studied. Dosing is driven by the phosphate-guided algorithm (and the intermittent 14-days-on/7-days-off schedule) rather than a CrCl rule.
Dialyzability & ESKD dosing
Highly protein-bound oral small molecule; not expected to be appreciably dialyzed. No validated ESKD dosing; the phosphate biomarker is confounded in ESKD.
Differential diagnosis
On-target FGFR-inhibitor hyperphosphatemia vs CKD-related hyperphosphatemia vs tumor lysis (with hyperuricemia/hyperkalemia/AKI). The early, dose-related, isolated phosphate elevation without AKI points to the drug.
Monitoring
- Serum phosphate at baseline and periodically (more often during up-titration/early cycles)
- Serum calcium and calcium-phosphate product
- Ophthalmologic exams for retinal detachment/serous retinopathy; routine creatinine
Key trials & series
- FIGHT-202 (registrational FGFR2-fusion cholangiocarcinoma)
- FIGHT-302 (first-line cholangiocarcinoma)
Clinical pearls
- Hyperphosphatemia is the FGFR-class signature; expect it, monitor phosphate, and treat with diet/binders before changing dose.
- Watch for rebound hypophosphatemia during the planned 7-day drug-free interval.
- Sustained elevation risks nephrocalcinosis — track the calcium-phosphate product, not phosphate alone.
Where it strikes
Nephron segments
Proximal Tubule
Bulk reabsorption + drug uptake (OCT2, OATs)
Injury signatures
Electrolyte Wasting
Beyond the kidney
Class-level context for the major non-renal toxicities of fgfr inhibitors.
Ophthalmic
Keratopathy, uveitis, retinopathy
- Central serous retinopathy
Dermatologic
Rash, HFS, SJS/TEN, vitiligo
- Nail/skin changes, hand-foot syndrome
Evidence
6 peer-reviewed references. Citation metadata via PubMed / NLM.
LandmarkPemigatinib for previously treated, locally advanced or metastatic cholangiocarcinoma: a multicentre, open-label, phase 2 study.Abou-Alfa GK et al. · Lancet Oncol 2020 · PMID 32203698Pivotal FIGHT-202 trial: hyperphosphatemia the most common adverse event.PMIDFGFR-targeted therapeutics: clinical activity, mechanisms of resistance and new directions.Katoh M et al. · Nat Rev Clin Oncol 2024 · PMID 38424198Mechanistic review linking FGFR-inhibitor hyperphosphatemia to FGFR1 inhibition of renal phosphate handling.PMIDManagement of Fibroblast Growth Factor Inhibitor Treatment-emergent Adverse Events of Interest in Patients with Locally Advanced or Metastatic Urothelial Carcinoma.Siefker-Radtke AO et al. · Eur Urol Open Sci 2023 · PMID 37101768Detailed FGFR-inhibitor phosphate management framework (binders, diet, dose modification) generalizable across the class.PMIDCalcinosis cutis dermatologic toxicity associated with fibroblast growth factor receptor inhibitor for the treatment of Wilms tumor.Arudra K et al. · J Cutan Pathol 2018 · PMID 30021048Demonstrates ectopic calcification from sustained FGFR-inhibitor hyperphosphatemia.PMIDSafety and efficacy of the pan-FGFR inhibitor erdafitinib in advanced urothelial carcinoma and other solid tumors: A systematic review and meta-analysis.Zheng X et al. · Front Oncol 2023 · PMID 36776367Class evidence supporting hyperphosphatemia as the dominant FGFR-inhibitor adverse event.PMIDSafety, pharmacokinetic, and pharmacodynamics of erdafitinib, a pan-fibroblast growth factor receptor (FGFR) tyrosine kinase inhibitor, in patients with advanced or refractory solid tumors.Nishina T et al. · Invest New Drugs 2017 · PMID 28965185Establishes hyperphosphatemia as an on-target FGFR pharmacodynamic effect, the shared class basis for pemigatinib.