Background: The introduction of cyclin-dependent kinase inhibitors (CDK4/6i) was a great advance in therapeutics for patients with estrogen receptor+/human epidermal growth factor receptor (HER2) locally advanced and metastatic breast cancer. Despite the increasing use of these agents, their adverse drug-related events have not yet been fully characterized. We describe the spectrum of cutaneous adverse reactions occurring in advanced breast cancer patients treated with cyclin-dependent kinase inhibitors, analyzing types, severity, time to onset, and possible treatment outcomes. Methods: We performed a multicentric retrospective study including patients with advanced breast cancer who developed cutaneous lesions during treatment with CDK4/6i in the period from June 2020 to June 2021. Patients > 18 years were recruited at eleven onco-dermatology units located in Albania (1), Argentina (1), France (1), Greece (3), Italy (3), and Spain (2). We evaluated patients’ epidemiological and clinical characteristics, types of cutaneous adverse events, their time to onset, and treatment outcomes. The severity of the skin reactions was assessed using the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 score. Results: Seventy-nine patients (median age: 62.3 years; range 39–83 years) were included in the study, and, collectively, we recorded a total of 165 cutaneous adverse events during follow-up visits. The most frequent cutaneous reactions were pruritus (49/79 patients), alopecia (25/79), and eczematous lesions (24/79). Cutaneous toxicities were usually mild in severity (>65%) and occurred after a median of 6.5 months. Only four patients (5%) required treatment discontinuation due to the severity of the skin lesions. The majority of the skin reactions were managed with topical treatments. Conclusions: To the best of our knowledge, we present the largest case series of cutaneous adverse events developing in advanced breast cancer patients treated with CDK4/6i. We showed that cutaneous toxicities are usually mild in severity, and manageable with standard supportive care; however, in selected cases, they can lead to treatment discontinuation with possible implications for patients’ clinical outcomes.

Background: There is a need for unified guidance in the management of acneiform rash induced by epidermal growth factor receptor inhibitors (EGFRi) among dermatologists.Objective: To establish unified international guidelines for the management of acneiform rash caused by EGFR inhibitors, based on an experts' Delphi consensus.Methods: The initiative was led by five members of the European Academy of Dermatology and Venereology Task Force ‘Dermatology for Cancer Patients’ who developed a questionnaire that was circulated to a group of 32 supportive oncodermatology experts in Europe, Canada, Argentina, the US States and Asia. The questionnaire consisted of 84 statements in total, regarding diagnosis and treatment of EGFRi‐induced acneiform rash. Experts responded to an anonymous 5‐point Likert scale survey. The coordinators collected the first‐round responses that were checked for consensus (≥75% agreement in positive [agree or strongly agree] or in negative [disagree or strongly disagree] vote). The statements that did not reach strong consensus in the first round were revised, according to experts' feedback, for a second‐round survey.Results: Strong consensus was reached in 75/84 (89.3%) of the statements, whilst moderate consensus was achieved in 6/84 elements. Key points include consideration of low‐dose isotretinoin for refractory grade II/III acneiform rash, use of topical steroid‐sparing agents like topical pimecrolimus in the maintenance phase and use of doxycycline in either 100 or 200 mg per day as prophylactic treatment. Interestingly, experts did not recommend topical antibiotics, neither for prevention, nor for treatment. Consensus failure in 3/84 objects is mostly related to the lack of robust data on these topics.Conclusion: This consensus offers crucial insights often overlooked by radiotherapists, general practitioners, dermatologists and oncologists, and it is expected to improve the management of oncologic patients treated with EGFRi in different settings and continents.