Background:Shadow cells, characterized by basaloid squamous cells with a distinct well-defined border and a central unstained area as a shadow of lost nuclei, are characteristic of pilomatricoma, a distinct neoplasm of hair matrix differentiation. The presence of shadow cells within tumor islands composed of follicular germinative cells of an otherwise classic basal cell carcinoma (BCC) has been considered as a distinct diagnostic category of BCC with matrical differentiation. We present a case of BCC with matrical differentiation in a trans-plant patient. To our knowledge, only 10 cases [Aloi et al. Am J Dermatopathol 1988; 10:509; Ambrojo et al. Am J Dermatopathol 1992; 14:293; Sagol et al. East J Med 1999; 4:37; Kwittken J. Cutis 2002; 69:57; Kim et al. Yonsei Med J 2003; 44:523]of BCC showing matrical differentiation have been reported. None have been reported arising on the background of immunosuppression. Methods:A 58-year-old male cardiac transplant patient with a nodule on the dorsum of left hand was studied. It arose and enlarged rapidly within a few months, causing irritation and bleeding. The nodule was surgically excised and submitted for histopathologic evaluation. The sections were prepared by hematoxylin and eosin (H&E) method. Results:The H&E-stained sections of the hand lesion revealed multiple nodular masses of basaloid follicular germinative cells. In some areas, there was peripheral palisading and stromal retraction artifact typical of classic BCC. In these areas, the tumor nodules were connected to the epidermis, whereas in others, it extended deep into the reticular dermis to the subcutaneous fat junction. Elsewhere, the majority of the tumor contained a population of shadow cells, similar to those in pilomatricoma, with basaloid-appearing matrical cells in the periphery. Trichohyaline granules were identified in the cytoplasm of many of the peripheral asaloid cells. These granules are one of the characteristic features of follicular matrix differentiation. Mitoses were rare. Areas of cystic degeneration were present throughout the tumor. There was no evidence of an infiltrating gro wth pattern, lymphovascular invasion, or sarcomatoid growth pattern. Conclusion :BCC with matrical differentiation is a distinct pathologic entity and a rare s ubtype of BCC featuring shadow and matrical cells, typically seen in pilomatrico ma, a benign hair matrix neoplasm. This tumor has not yet been reported in an im munosuppressed transplant patient. Background: Shadow cells, characterized by basaloid squamous cells with a distinct well-defined border and a central unstained area as a shadow of lost nuclei, are characteristic of pilomatricoma, a distinct neoplasm of hair matrix differentiation. The presence of shadow cells within tumor islands composed of follicular germinative cells of an otherwise classic basal cell carcinoma (BCC) has been considered as a distinct diagnostic category of BCC with matrical differentiation. We present a case of BCC with matrical differentiation in a trans-plant patient. To our knowledge, only AmioDermatopathol 1992; 14: 293; Sagol et al. East J Med 1999; 4:37; Kwittken J. Cutis 2002; 69: 57; Kim et al. Yonsei Med J 2003; 44: 523] of BCC showing matrical differentiation have been reported. None have been reported arising on the background of immunosuppression. Methods: A 58-year-old male cardiac transplant patient with a nodule on the The arose and enlarged recently within a few months, causing irritation and bleeding. The nodule was surgically excised and submitted for histopathologic evaluation. The sections were prepared by hematoxylin and eosin (H & E) method. Results: The H & E -stained sections of the hand lesion revealed multiple nodular masses of basaloid follicular germinative cells. In some areas, there was peripheral palisading and stromal retraction artifact typical of classic BCC. In these areas, the tumor nodules were connected to the epidermis, whereas in others , it extended deep into the reticular dermis to the subcutaneous fat junction. Elsewhere, the majority of the tumor contained a population of shadow cells, similar to those in pilomatricoma, with basaloid-appearing matrical cells in the periphery. Trichohyaline granules were identified in the cytoplasm of many of the peripheral asaloid cells. These granules are one of the characteristic features of follicular matrix difAreas of cystic degeneration were present throughout the tumor. There was no evidence of an infiltrating gro wth pattern, lymphovascular invasion, or sarcomatoid growth pattern. Conclusion: BCC with matrical differentiation is a distinct pathologic entity and a rare s ubtype of BCC featuring shadow and matrical cells, typically seen in pilomatrico ma, a benign hair matrix neoplasm. This tumor has not yet been reported in an im munosuppressed transplant patient.