Introduction: The development of cutaneous neoplasms at immunization sites following vaccination is uncommon, and only few have been reported in the literature worldwide. We report an unusual case of an ulcerated giant dermatofibroma that developed as a chronic nonhealing plaque in the immunization scar of a young boy after vaccination. Case Report: A 13-month-old Chinese boy presented with an unusual skin reaction on the vaccination site at the right anterolateral thigh following a routine intramuscular injection of ‘5-in-1’ (diphtheria, tetanus, pertussis, polio and Haemophilus influenzae B) vaccine at 4 months of age. The immunization site developed a slightly raised papule with a central punctum that progressively grew in size, ulcerated and showed occasional bleeding over a span of 9 months. On follow-up, the lesion showed a chronic granulomatous reaction with surrounding induration and a central scarring. The right inguinal lymph node was palpable. Ultrasound of the lesion showed only nonspecific focal skin thickening. An incisional skin biopsy with careful histopathological evaluation revealed microscopic features consistent with an ulcerated giant dermatofibroma. Conclusion: Neoplastic development in immunization scars following vaccination is a rare occurrence and, hence, makes this case a diagnostic challenge. A high index of suspicion is crucial in atypical presentations of a common skin lesion, as typified by this case. Careful history taking and clinicopathological correlation of clinical findings with gross and microscopic findings along with targeted immunohistological staining is often essential to aid early diagnosis.

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