Supplementary Material for: Malignant Hidroacanthoma Simplex: A Case Report

Introduction Malignant hidroacanthoma simplex (MHS) is an exceedingly rare cutaneous neoplasm with limited documented cases. This report highlights a distinctive case of MHS with prolonged clinical evolution, emphasizing its diagnostic challenges and management outcomes. Case Presentation A 64-year-old female presented with a right lumbar mass persisting for over two decades, exhibiting progressive enlargement in the past five years. Clinical examination revealed a solitary reddish-brown proliferative plaque (3.5 cm × 4.0 cm) on the right waist, characterized by irregular borders, a rough surface, and reddish-brown crusts. Histopathological findings included hyperkeratosis, irregular epidermal hyperplasia, hypertrophic stratum spinosum, and tumor cells displaying pale eosinophilic cytoplasm, vacuolated nuclei, small nucleoli, and atypical mitotic figures. Notably, tumor cells were confined to the epidermis without dermal invasion. The patient underwent local extended excision, and postoperative surveillance over 15 months demonstrated no evidence of recurrence or lymph node metastasis. Conclusion This case underscores the indolent yet locally persistent nature of MHS. Complete surgical excision remains the cornerstone of management, with favorable outcomes achievable in absence of dermal infiltration. Long-term follow-up is critical to monitor potential recurrence.

引言：单纯性恶性汗腺棘皮瘤（Malignant hidroacanthoma simplex, MHS）是一种极为罕见的皮肤肿瘤，目前文献报道的病例数量有限。本案例报告1例病程迁延的特殊MHS病例，着重阐述其诊断难点与治疗结局。

病例报告：1例64岁女性患者，右侧腰部肿物病程已二十余年，近5年出现进行性增大。体格检查示右侧腰部可见单发红棕色增生性斑块（3.5 cm × 4.0 cm），边界不规则，表面粗糙，覆有红棕色痂皮。组织病理学检查可见角化过度、表皮不规则增生、棘层肥厚；肿瘤细胞胞质呈淡嗜酸性，核空泡状，核仁小，可见病理性核分裂象。值得注意的是，肿瘤细胞仅局限于表皮内，未侵犯真皮。患者接受局部扩大切除术，术后15个月的随访未发现复发及淋巴结转移。

结论：本案例进一步证实MHS呈惰性但局部迁延的病程特点。完整手术切除仍是治疗的核心手段，未出现真皮浸润者可获得良好预后。长期随访对于监测潜在复发至关重要。