Pathologic Prognostic Factors of Pineal Parenchymal Tumor of Intermediate Differentiation.

INTRODUCTION: Pineal parenchymal tumor of intermediate differentiation (PPTID) is an uncommon tumor of the pineal gland. Although this behaves as a grade II/III tumor, the exact clinical behavior is not well known. There is no well-established pathologic factor that can predict the behavior of PPTID.

AIM AND OBJECTIVE: The aim of this study was to determine the pathologic prognostic factors in PPTID.

MATERIALS AND METHODS: All PPTID cases diagnosed between 2006 and 2016 were analyzed retrospectively. Immunohistochemistry for synaptophysin, neurofilament protein (NFP), glial fibrillar acid protein, NeuN, and Ki-67 were performed in all cases. Cases were classified arbitrarily into low grade (mitosis <4/10 hpf and Ki-67 <5%) and high grade (mitosis ≥4/10 hpf and Ki-67 ≥5%). Clinical details including follow-up information were retrieved from the patients' files.

RESULTS: A total of 16 patients (6 low grade and 10 high grade) were included in this study. The age ranged from 2 to 55 years (average, 28.2) with a mild male preponderance (male:female, 1.67:1). All cases showed strong and diffuse positivity for synaptophysin. Focal NFP positivity was seen in 2 low-grade and 3 high-grade tumors. Only 2 cases showed focal NeuN positivity. Average Ki-67 index was 1.7% and 12.6% in low-grade and high-grade tumors, respectively. All patients with low-grade tumor were alive without recurrence. Among the patients with high-grade tumors, 2 had local recurrence, 1 had spinal metastasis, and 3 patients died.

CONCLUSION: Mitosis and Ki-67 proliferation index are the most important pathologic prognostic factors in PPTID. NFP expression does not carry any prognostic significance.