Clinically aggressive solid pseudopapillary tumors of the pancreas: a report of two cases with components of undifferentiated carcinoma and a comparative clinicopathologic analysis of 34 conventional cases.

Solid pseudopapillary tumors (SPTs) are unusual neoplasms of the pancreas of uncertain histogenesis that occur mostly, but not exclusively, in young women. The pathologic features and immunophenotype of SPT are unique and well characterized. Despite its low malignant potential, proximately 15% of patients with SPT develop metastatic disease, mostly involving the liver or peritoneum. Even in the presence of disseminated disease, the clinical course is usually protracted, and the overall 5-year survival is reportedly 97%. We have encountered 2 cases of SPT possessing unusual pathologic features and exhibiting an aggressive clinical course. At the time of presentation, 1 patient had liver metastasis, and the other had a lymph node metastasis and developed liver metastases within 3 months. Both died of disease at 6 and 16 months, respectively, following the initial diagnosis. Review of other cases of SPT treated at Memorial Sloan-Kettering Cancer Center (New York, NY) revealed that 5 of 34 cases (15%) with conventional histologic features developed liver metastases. In contrast to the 2 cases reported here, all 5 patients survived for a mean of 106 months (39-193 months), and only 2 died of disease 5 and 10 years, respectively, following the initial resection. The pathologic features of the two rapidly fatal cases, which might have been indicative of their aggressive behavior, included a diffuse growth pattern, extensive tumor necrosis, significant nuclear atypia, an unusually high mitotic rate (35-70/50 high power fields), and in one a component of sarcomatoid carcinoma. However, regions displaying the typical histologic features of SPT were also evident. Abnormal beta-catenin distribution and markedly increased MIB1 expression were detected by immunohistochemistry in both cases. The immunohistochemical staining patterns were otherwise similar to those of conventional SPTs. Although precise pathologic criteria suggesting a high risk for aggressive behavior are uncertain, recognition of some of the unusual pathologic features displayed in these 2 cases may be useful in the prediction of potentially more aggressive SPTs. The possibility that these tumors represent high-grade malignant transformation of a conventional low-grade SPT is proposed.