Metastatic hormone receptor-positive breast cancer with paraneoplastic eosinophilic fasciitis

What happened, in summary

This 79-year-old woman had lived with breast cancer for 19 years before developing an unusual skin and soft-tissue complication in her left leg. Her breast cancer was hormone receptor-positive, with ER and PR positivity. Earlier treatment had included an aromatase inhibitor, followed by capecitabine, which was stopped because of hand-foot syndrome. After stopping capecitabine, she noticed swelling and hardening in the left leg. Over 3 months, she developed a bothersome, itchy rash with redness, edema, and an orange-peel texture, but no signs of infection. Her eosinophil count rose, while Doppler ultrasound ruled out thrombosis. Skin biopsy showed hyperkeratosis, dermal fibrosis, eosinophil-rich inflammation, and thickened fibrous septa around small subcutaneous fat lobules. These findings supported eosinophilic fasciitis, considered paraneoplastic because of the cancer context and timing. She was treated with prednisone 0.75 mg/kg/day, tapered over 40 days. Within 1 month, the skin lesions completely resolved and the eosinophil count decreased markedly. Three months later, eosinophilic fasciitis returned in the lower third of the left leg and was again confirmed histologically. During an oncology check-up, she was diagnosed with pelvic metastasis from breast cancer. Treatment then combined doxorubicin and vinorelbine with another prednisone course, again starting at 0.75 mg/kg/day and tapering over 30 days. The skin lesions quickly went into remission. As of February 2024, 6-month follow-up showed no further eosinophilic fasciitis recurrence and no signs of cancer progression. This response supported a clinical link between active malignancy control and improvement in the inflammatory fasciitis in the same leg.