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Abstract：
Pilomatrixoma is an uncommon, benign tumor with differentiation towards both the hair matrix and cells arising in the cortex, most frequently appearing in the first or second decade of life. In rare instances, pilomatrixomas can show malignant transformation. Pilomatrix carcinoma is extremely uncommon and has traditionally been considered a tumor of low malignant potential; however, a high local recurrence rate has been reported. There is a paucity of literature on these lesions, with only a few reports describing the spectrum of malignant changes seen in these lesions. In this case report, we present a case of pilomatrixoma in an adult patient showing atypical features. While the tumor is small, there are focal features that suggest progression to malignancy, but do not fulfill the criteria for pilomatrix carcinoma. These focal atypical features include a focal infiltrative pattern at the periphery, with a variable cytological atypia and an increased mitotic rate, up to five mitotic events/high-power field. Irregular foci of central necrosis (comedonecrosis) were present in several lobules. Some of the features identified were similar to a subset of pilomatrixoma, known as \"proliferating pilomatrixoma.\" However, our case did not have the diffuse changes or larger size that has been frequently reported in \"proliferating pilomatrixoma.\" In conclusion, given the lack of focality of the changes, the lesion in our case is best described as a pilomatricoma with atypical features. Furthermore, our case may highlight the need to ensure close clinical follow-up for these lesions with unexpected atypical features that raise concern of recurrence and malignant transformation.
摘要：
皮房瘤是一种罕见的，向毛发基质和皮质中产生的细胞分化的良性肿瘤，最常出现在人生的第一个或第二个十年。在极少数情况下,毛曲菌瘤可表现为恶性转化。Pilomatrix癌极为罕见，传统上被认为是低恶性潜能的肿瘤；然而，据报道，局部复发率很高。关于这些病变的文献很少，只有少数报告描述了在这些病变中看到的恶性变化的范围。在这个案例报告中,我们介绍了一例成年患者的毛囊房瘤，表现出非典型特征。虽然肿瘤很小，有局灶性特征表明进展为恶性肿瘤，但不符合毛发上皮癌的标准。这些局灶性非典型特征包括周边的局灶性渗透模式，具有可变的细胞学异型性和增加的有丝分裂率，多达五个有丝分裂事件/高功率场。在几个小叶中存在不规则的中央坏死灶（粉刺坏死）。确定的一些特征类似于毛结肠瘤的一个子集，被称为“增殖的毛心房瘤”。\"然而,我们的病例没有扩散变化或更大的体积,这在增生性毛囊房瘤中经常报道.“总之，鉴于变化缺乏针对性，在我们的病例中，病变最好被描述为具有非典型特征的毛囊瘤。此外，我们的病例可能强调需要确保对这些具有意外非典型特征的病变进行密切的临床随访,这些特征会引起复发和恶性转化的关注.
