Evaluation of posttransplantation malignancies compared with de novo tumors.

It is uncertain whether tumors arising in transplant patients resemble ones that develop de novo in pathogenesis, morphology, and behavior. This study sought to investigate some clinical, morphological, and immunohistochemical features of several posttransplantation malignancies compared with similar de novo tumors. The study group consisted of 40 malignant tumors encountered in 1350 transplant patients (1229 kidneys, 113 livers, 8 hearts) between 1986 and 2006. Tumors with 3 or more examples were compared with randomly selected controls. These included Kaposi's sarcoma (n=14); extranodal lymphoma (n=9); squamous cell carcinoma (n=6); and nodal lymphoma (n=3). The variables that were analyzed were the localization, predisposing lesions, degree of differentiation, and host response. For lymphomas, we also determined histological subtype, origin, and Ki-67 proliferation index. Most tumors (36/40, 90%) occurred in patients with renal transplants. However, the relative frequency was higher among liver transplant cases (3.53% vs 2.92% for kidney transplants). No malignancy was seen in heart transplant cases. Squamous cell carcinomas were better differentiated (P<.05) compared with controls and they were more frequently associated with precursor lesions (P<.05). Kaposi's sarcomas involved internal organs more frequently in posttransplant patients, and the Ki-67 proliferation index was higher in posttransplantation nodal lymphomas. However, these factors were not significantly different (P>.05). Our findings suggested that certain posttransplantation malignancies display unique characteristics compared with their de novo counterparts.