Table 4.

Monitoring of CDK4/6 inhibitor-associated side effects.

	Hematologic Side Effects	Gastrointestinal Toxicity	Liver Enzyme Elevation	Pulmonary Embolism	QT Prolongation
Symptoms	Fatigue, shortness of breath, increased tendency to bleed, and/or bruise [82]	Diarrhea, nausea, vomiting* [12, 13, 14]	Weight loss, jaundice, dark urine, itching, abdominal swelling [64]	Shortness of breath, chest pain, cough, rapid breathing, rapid heart rate [38, 66]	Palpitations, fainting episodes [69]
Clinical assessment	Complete blood counts [7, 38]	Electrolyte levels [60]	Liver function tests [64]	Monitor patient symptoms [38]	ECG [83]
Crucial time window	2 weeks after drug administration in treatment Cycles 1 and 2 (palbociclib and ribociclib) [34, 38, 53]	1 week after drug administration (abemaciclib)*	Throughout treatment [14]	Throughout treatment [38]	First 4 weeks of treatment [14]
Frequency of monitoring	Start of each treatment cycle. Additional assessments during Cycles 1 and 2 [7, 38]	Throughout treatment*	Throughout treatment [14]	Throughout treatment [38]	Throughout treatment [14]
Additional risk factors	Infections, fever, Asian ethnicity, low baseline neutrophil count [53, 82]	Fever, dizziness, abdominal pain [60]	Concomitant medication [84]	Deep-vein thrombosis [66]	Diarrhea, vomiting, concomitant medication [69]

CDK, cyclin-dependent kinase; ECG, electrocardiogram.

*Dickler, M.; Tolaney, S.; Rugo, H.; Cortes, J.; Diéras, V.; Patt, D.A.; Wildiers, H.; Frenzel, M.; Koustenis, A.; Baselga, J. MONARCH 1: Results from a phase II study of abemaciclib, a CDK4 and CDK6 inhibitor, as monotherapy, in patients with HR+/HER2- breast cancer, after chemotherapy for advanced disease. J. Clin. Oncol., 2016, 34(suppl), Abstract 510 (Oral presentation).