The patients with primary PCL showed better prognosis than those with secondary PCL.

Primary PCL might be a differently developed disease from MM.

In diagnosing PCL, it is important to differentiate primary PCL from secondary PCL for the prediction of prognosis.

Ten cases of PCL (7 cases of primary PCL and 3 cases of secondary PCL) and 20 sex- and age-matched cases of MM were compared.