BI14 Case series: exploring the link between psoriasis and cyclin-dependent kinase 4/6 inhibitors in breast cancer treatment

Abstract Psoriasis is a chronic, immune-mediated, inflammatory skin disorder characterized by abnormal keratinocyte hyperproliferation. Proinflammatory cytokines including interleukin (IL)-23, IL-17, IL-22 and tumour necrosis factor-α are considered primary mediators, and have been therapeutic targets for treatment. Recent studies have shown that cyclin-dependent kinase (CDK) inhibitors interfere with keratinocyte proliferation and modulate the release of cytokine production, and may play a role in the pathogenesis of psoriasis. CDK4/6 inhibitors have been widely used in the treatment of hormone receptor-positive, human epidermal growth factor receptor (HER)2-negative breast cancer due to their ability to arrest tumour cell proliferation. Although they are generally well tolerated, reports of psoriasis have been documented with the use of CDK inhibitors. With the increasing interest in small-molecule treatment for various conditions including cancers and infectious and inflammatory diseases, we would like to highlight two recent cases at our centre. A 64-year-old, female patient with no prior history of psoriasis or inflammatory dermatoses was diagnosed with metastatic, invasive ductal carcinoma, grade 3 oestrogen receptor (ER)+, HER2− in January 2024. She was initiated on palbociclib and letrozole treatment in April 2024. In December 2024 (8 months after treatment initiation), the patient developed discrete, erythematous, plaques with silvery scale on her bilateral forearms and lower limbs, with thick plaques on her frontal scalp. A diagnosis of psoriasis was confirmed clinically. A 55-year-old woman had grade 2 ER+, HER2− breast cancer diagnosed in 2012. She was commenced on ribociclib and letrozole for relapsed metastatic liver disease in April 2023. The patient developed a cutaneous eruption in August 2023, 4 months after treatment initiation. On examination there were scaly psoriasiform small plaques on the bilateral extensor upper and lower limbs. A diagnosis of psoriasis was confirmed histologically. Treatment with ribociclib was temporarily held and restarted at a lower dose after 3 months. The psoriasis became more prominent on restarting treatment. These cases highlight the potential role of CDK4/6 inhibitor involvement in psoriasiform eruptions. Understanding the role of CDK4/6 inhibition and the link with psoriasis is important for optimizing therapeutic choices for patients with cancer with pre-existing or newly developed psoriasis. Given the increasing use of CDK4/6 inhibitors in cancer treatment, clinicians should be vigilant of the potential increased prevalence of psoriasis experienced in this patient cohort.