FIGURE 1

Development of thymomas in the lck-pX thymuses transplanted into the subcapusular space of the recipient kidney, and the malignant transformation. (a) At 3 months after the transplantation, a tumor (arrowhead) developed in the transplanted lck-pX thymus. (b) Microscopically, the tumor (arrowheads) showed the same histological features as original thymomas in lck-pX rats. (c) Metastases to the lungs (arrowheads). (d) Peritoneal disseminations and a large tumor formation adjacent to the kidney (arrowheads) were observed when the tumor was incubated for another 3 months. Figures are from representative rats at 3 and 6 months after the transplantation (n=5). (e, f) Histopathologically, nuclear atypia and mitosis (e, arrowhead) were prominent in the transformed thymomas compared with those in the originals (f) (HE staining). (g, h) Many nuclei of cells positively stained with anti-Ki-67 antibody were found in the transformed thymomas (g, brown staining in nuclei) but few in the originals (h). Bars in microscopic photos indicate 250 m (b), and 50 m (e–h). (i) Comparison of Ki-67 index between the transformed (n=5, closed circles) and original (n=9, open circles) thymomas. Bars indicate meanstandard deviation. ^*Student's t-test was used for statistical analysis.