We herein report three cases of multiple myeloma (MM), in which no M component was detected in serum or urine; however, the serum free light chain (sFLC) assay showed an excess of sFLC-κ and a high κ/λ ratio. The first case was a man in his fifties with multiple osteolytic lesions and hypercalcemia. The immunofixation of serum revealed no M component and urinary protein was below the detection level, while sFLC-κ was 10,700.0 mg/L (reference range, 3.3 to 19.4 mg/L) and the κ/λ ratio was 672.96 (reference range, 0.26 to 1.65). Although he responded to bortezomib and dexamethasone followed by high-dose melphalan with autologous hematopoietic stem cell transplantation, he relapsed with the features of plasma cell leukemia. The second case was a woman in her forties with multiple bone involvement. The immunofixation of serum and urine was negative, while sFLC-κ was 1,610.0 mg/L and the κ/λ ratio was 217.57. She was treated with bortezomib, lenalidomide, and dexamethasone. The third case was a woman in her seventies with paraplegia due to a vertebral tumor. Immunofixation was negative, sFLC-κ was 1580.0 mg/L, and the κ/ λ ratio was 141.07. Bone marrow in each case contained 63.8, 39.8, and 7.4% myeloma cells in which the κ light chain was expressed in the cytoplasm, as revealed by multicolor flow cytometry. Fluorescence in situ hybridization of myeloma cell nuclei revealed the presence of the CCND1-immunoglobulin heavy chain fusion gene (IGH) indicative of t(11;14)(q13;q32), but showed variant hybridization signal patterns. These three cases matched the criteria of recently proposed sFLC-only MM and were characterized by multiple bone involvement, the lack of significant anemia and impaired renal function, an immature myeloma cell morphology, and the CCND1-IGH fusion gene. These results support the routine use of the sFLC assay for a work-up when a patient is suspected of having a plasma cell disorder.

A Taiwanese woman in her fifties presented with a feculent odor and eructation. Her white cell count was 15.56 × 10³/μL, albumin 3.2 g/dL, lactate dehydrogenase 335 U/L, C-reactive protein 4.8 mg/dL, and soluble interleukin-2 receptor 1,398 U/mL (reference range, 145 to 519 U/mL). Computed tomography (CT) revealed a left upper quadrant tumor encompassing the greater curvature of the stomach and splenic flexure of the colon to create gastrocolic fistula, and CT colonography confirmed communication between the two luminal organs. Upper gastrointestinal endoscopy showed a submucosal tumor at the greater curvature of the stomach and the orifice of the fistula was detected at the top of the tumor. Biopsies revealed the non-germinal center B-cell–like type of diffuse large B-cell lymphoma and lymphoma cells carried the BCL6 rearrangement. She was treated with R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone) chemotherapy under total parenteral nutrition and achieved a complete response after 6 cycles of R-CHOP; no perforation or bleeding complications occurred during the course of treatment. To the bestof our knowledge, this is the first report of DLBCL presenting with gastrocolic fistula that was successfully treated with R-CHOP chemotherapy, avoiding surgical intervention.

Gain-of-function mutations of MYD88 and CD79B genes have been reported to lead to constitutive activation of the nuclear factor (NF)-κB pathway, thereby playing an important role in the development of malignant B-cell-type lymphoma. We herein investigated MYD88^L265P and CD79B^Y196 mutations by polymerase chain reaction-based techniques in a total of 141 cases of different types of B-cell lymphoma, and correlated the mutations with B-cell lymphoma category, primary anatomical site of the disease, class of immunoglobulin heavy chain expressed on the cell surface, and rearrangement of the BCL2, BCL6, and MYC genes. As a result, MYD88^L265P mutation was detected in 18 (22%) of 81 cases of diffuse large B-cell lymphoma (DLBCL), 2 (100%) of 2 cases of lymphoplasmacytic lymphoma, and 1 (5%) of 20 cases of unclassifiable B-cell lymphoma. CD79B^Y196 mutation was found in 14 (17%) DLBCL cases, and 9 DLBCL cases carried both mutations, but no mutation was found in follicular lymphoma, marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma), or mantle cell lymphoma. MYD88^L265P/CD79B^Y196 mutations were significantly associated with DLBCL of the non-germinal center B-cell-like (non-GCB) subtype, and the mutations were preferentially found in DLBCL that developed in particular extranodal sites, e.g. brain, testis, and nasal cavity/paranasal sinuses. Expression of the μ heavy chain was associated with MYD88^L265P/CD79B^Y196 mutations, and that of the γ or α heavy chain was associated with the lack of mutation and GCB phenotype. Of 23 cases with MYD88^L265P/CD79B^Y196 mutations, 7 had rearrangement of either BCL2, BCL6, or MYC, and one had both BCL2 and BCL6 mutations, suggesting that MYD88^L265P/CD79B^Y196 mutations and BCL2/BCL6/MYC rearrangements are not necessarily exclusive. As MYD88/CD79B mutations were found to correlate with the response to Bruton's tyrosine kinase inhibitor ibrutinib, detection of mutations will become necessary to select appropriate targeting agents in the treatment of B-cell lymphoma.

We developed multimodal tests to support the diagnosis of angioimmunoblastic T-cell lymphoma (AITL), for which the cell of origin was previously determined to be follicular helper T-cells in the germinal center and RHOA^G17V has been reported as a highly recurrent mutation. In this study, we subjected clinical specimens from 5 patients with AITL to multicolor flow cytometry (FCM) and polymerase chain reaction (PCR)-based assays. We found that lymphoma cells in the 5 cases were invariably characterized by diminished or loss of CD3 expression compared with non-neoplastic T-cells. CD10 was expressed in lymph node specimens in 4 cases; however, the proportion of CD10+ neoplastic T-cells varied. Multicolor FCM using a 10-color antibody panel detected neoplastic T-cell populations in all cases, comprising 2 to 41% within each clinical specimen. We next developed three PCR-based assays for detection of the RHOA^G17V mutation, and demonstrated that allele-specific (AS)-PCR was capable of detecting as low as 0.1% RHOA^G17V mutant DNA. Using this sensitive AS-PCR, the mutation was found in 4 cases, whereas one was negative. We propose the sequential diagnostic use of multicolor FCM for immunophenotypic and quantitative assessment of lymphoma cells and AS-PCR for the detection of RHOA^G17V mutation.