CASE HISTORY

4-year-old boy from Venezuela, who presented with a large, focally ulcerated, soft tissue mass on the right side of his lower chest/upper abdomen.

Imaging studies showed a large soft tissue mass on the right side of the patient's lower chest/upper abdomen, adjacent to the right lobe of the liver.

Several benign and malignant diagnostic possibilities were entertained, including rhabdoid tumor among others, and the case was eventually sent to Dr. Zambrano for further evaluation, courtesy of Dr. María Elena Viloria (pathologist, Maracaibo, Venezuela).

On low power view, the tumor was vastly composed of sheets of large epithelioid cells with abundant eosinophilic (pink) cytoplasm. 

On higher power, a large proportion of the cells were noticed to have eccentric nucleus with prominent eosinophilic nucleoli, suggesting the possibility of a rhabdoid tumor, a highly aggressive malignant tumor.

However, expression of INI-1 and BRG1 proteins was retained (normal), making a diagnosis of rhabdoid tumor highly unlikely.

In addition, in many areas, the tumor cells were noticed to be disposed in a pseudoalveolar pattern, with nests of discohesive cells separated by thin fibrovascular septa.

Histochemical studies revealed numerous PAS-positive diastase-resistant crystals and granules in the cytoplasm of neoplastic cells.

Based on these findings, a diagnosis of alveolar soft part sarcoma was given, a tumor which, in spite of being malignant, has an overall better prognosis than rhabdoid tumor, a more aggressive tumor with very poor prognosis.