Primary lymphoma of peripheral nerve: report of four cases.

Lymphoma presenting as a solitary tumor of peripheral nerve is exceedingly rare, with only six previously reported cases. The authors describe an additional four cases of primary lymphoma of peripheral nerve involving the sciatic nerve (two cases), the radial nerve, and the sympathetic chain and spinal nerve. The patients were two men and two women with an average age of 55.5 years. All tumors were high-grade B-cell lymphomas. Two patients experienced relapse of disease with involvement of other nervous system sites and died of lymphoma. One patient is alive with stable local disease at 57 months. The fourth patient is alive with no evidence of disease at 54 months. Expression of neural cell adhesion molecule (CD56) has been reported to correlate with an increased incidence of central nervous system involvement in peripheral T-cell lymphoma; all their cases were CD56 negative. Recent reports indicate a high proportion of primary brain lymphomas show loss of CDKN2A/p16 gene expression. Therefore, CDKN2A/p16 was evaluated in their patients both by polymerase chain reaction and by immunohistochemistry for the p16 protein. The authors found homozygous deletion of the CDKN2A/p16 gene in one of three patients studied, confirmed immunohistochemically by absent staining for p16. The fourth patient showed absent staining for p16, suggesting inactivation of the gene in this case as well. The two patients with p16 loss both died of lymphoma, whereas the two patients with normal p16 expression are alive. Primary lymphoma of peripheral nerve is a rare neoplasm, usually of large B-cell type, has a variable prognosis, and appears to have less consistent loss of p16 expression than primary central nervous system lymphoma.