Unilateral Calf Swelling and Skin Induration During Pembrolizumab-Based Neoadjuvant Therapy for Triple-Negative Breast Cancer: A Case Report

Eosinophilic fasciitis (EF) is a rare fibro-inflammatory disorder that has been reported following immune checkpoint inhibitor (ICI) therapy.We report the case of a woman in her 70s with locally advanced triplenegative breast cancer (TNBC) who developed acute unilateral calf pain, erythema, swelling, and woody skin induration approximately four months after commencing neoadjuvant pembrolizumab-based therapy.Investigations demonstrated peripheral eosinophilia and a normal creatine kinase (CK) level.Pembrolizumab was withheld because of initial concern for ICI-associated myositis, and oral prednisolone was commenced at 60 mg daily (approximately 1 mg/kg).Magnetic resonance imaging (MRI) performed 19 days after corticosteroid initiation showed mild subcutaneous soft-tissue edema without evidence of myositis or characteristic fascial abnormalities.Pain, erythema, and swelling improved within days, and the eosinophil count fell during corticosteroid treatment, although skin induration persisted.Rheumatology assessment supported a clinical working diagnosis of suspected EF.Biopsy was not pursued in view of clinical improvement.Pembrolizumab was permanently discontinued after multidisciplinary discussion.Prednisolone was gradually tapered and discontinued over approximately four months without the need for additional immunosuppression.At last review, five months after symptom onset, she remained off corticosteroids, with resolution of pain, erythema, and swelling and only residual skin induration.Paclitaxel-associated sclerosis and morphoea profunda remained competing explanations, and attribution to pembrolizumab was possible rather than established.This case highlights the importance of specialist assessment of unexplained limb swelling and woody skin induration during combination anticancer therapy.Normal CK levels and corticosteroid responsiveness do not establish EF.