Spontaneous regression of plasmablastic lymphoma in an elderly human immunodeficiency virus (HIV)-negative patient

An 80-year-old man was referred to our hospital owing to rapid growth of a gingival tumor in the right maxillary second molar region. He had suffered from repeated gingival swelling of this region for 8 months before his visit. Following a diagnosis of apical periodontitis, his right maxillary second molar was extracted 6 weeks before his visit. After an additional mucosal curettage to treat unsuccessful wound healing, the gingiva at the extraction site began to rapidly grow in size. The patient had no significant past medical history including autoimmune diseases and had not taken any immunosuppressive medication.

A physical examination revealed an exophytic gingival tumor in the right maxillary second molar (Fig. 1a). This soft elastic tumor was well circumscribed and bled easily. Computed tomography showed that the tumor measured 26 × 23 × 16 mm and was confined in the alveolar bone. Progression of the tumor to the maxillary antrum was not observed, nor was lymph node swelling. ¹⁸F-fludeoxyglucose positron emission tomography (FDG-PET) showed elevated FDG uptake in the right maxilla with a maximum standardized uptake value of 29.29 (Fig. 1b). Abnormal FDG uptake at other sites was not noted. Serum levels of lactate dehydrogenase (208 IU/L) and soluble interleukin-2 receptor (177 U/mL) were normal, and a screening test for HIV was negative. Serological tests for EBV were also performed (Table 1).

A biopsy of the lesion showed a solid tumor with an ulcertic surface (Fig. 2a). The tumor was characterized by monomorphic neoplastic proliferation of large plasmacytoid and immunoblastic cells with prominent nucleoli (Fig. 2b). Necrosis and giant cells with features similar to those of Hodgkin and Reed/Sternberg cells were not observed. Immunohistochemical immunophenotyping analysis showed that the neoplastic cells were positive for LCA and CD138 and negative for CD20, CD79a, PAX5, CD3, CD5, CD10, CD15, CD56, ALK, LMP1, and EBNA2 (Fig. 2c, d). CD30 expression was not determined. Forty percent of the tumor cells expressed c-Myc, and the Ki-67 labeling index was >80 % (Fig. 2e). As determined via in situ hybridization, neoplastic cells were EBV-encoded RNA (EBER)-positive (Fig. 2f). Although cytoplasmic κ and λ light chains were not detected via in situ hybridization (Fig. 2g, h), clonal IgH chain gene rearrangement was detected via polymerase chain reaction (PCR) (Fig. 2i). Because the patient had no immunosuppressive condition other than advanced age, he was diagnosed with PBL-E, and surgical excision was scheduled.

After the biopsy, however, the tumor began to decrease in size. Surgical excision was performed 40 days after the biopsy, although the exophytic tumor had apparently disappeared (Fig. 1c). A surgical specimen showed infiltration of CD138-positive plasma cells and polymorphic inflammatory cells, including numerous foamy macrophages (Fig. 3a, b). The plasma cells expressed cytoplasmic immunoglobulins (κ and λ light chain) with no light chain restriction, and the results of EBER in situ hybridization were negative (Fig. 3c–e). There was no evidence of a residual neoplastic lesion.

Serological testing for EBV was performed 4 days after surgery, and EBV-DNA was detected in whole blood via real-time PCR (Table 1). FDG-PET imaging 102 days after the biopsy showed no abnormal FDG uptake (Fig. 1d), suggesting that the neoplastic lesion had clinically disappeared completely. The patient has thus far been followed-up for 5 months with no sign of relapse.

Written informed consent was obtained from the patient for publication of this report and any accompanying images.