This is the first study that analyzed the diagnostic utility of IGH and TCR rearrangements in clonality analyses in addition to MALT1 translocation in BALF of patients with clinically suspected pulmonary lymphoma. In our study, the sensitivity and specificity of IGH rearrangement results for B-cell lymphoma diagnosis were 88.9% and 90.0%, respectively. All patients with B-cell lymphoma were negative for TCR rearrangements, and the specificity of combined IGH rearrangement-positive and TCR rearrangement-negative results for the B-cell lymphomas diagnosis was 96.0%. The sensitivity and specificity of MALT1 translocation testing for MALT lymphoma diagnosis were 28.6% and 100%, respectively. These findings suggest that the combined detection of IGH and TCR rearrangements in BALF cells is useful for the screening and diagnosis of B-cell lymphomas and that analysis of specific genes such as MALT1 can improve the diagnostic accuracy.
It is difficult to detect pulmonary lymphomas using small tissue samples obtained by TBLB or CT-guided lung biopsy, and 55.7–100% of patients need surgical interventions for definitive diagnosis(1, 6, 8–10). In a retrospective review of 24 patients with pulmonary lymphomas, only 3 of 13 patients with pulmonary MALT lesions underwent complete surgical resection, whereas the others received chemotherapy (9). In another retrospective study of 61 patients with pulmonary MALT lymphomas, no differences were observed in the time to progression between patients who underwent invasive surgical resection and those who received chemotherapy (8). Thus, the development of molecular methods that allow making accurate diagnosis using small tissue samples is essential to help avoid invasive procedures. In the present study, 66.7% of patients with B-cell lymphomas were diagnosed without SLB, including 2 patients positive for both IGH rearrangements and MALT1 translocations, indicating that the combined detection of these genetic aberrations can provide a more accurate diagnosis through a less invasive procedure.
The usefulness of detecting IGH rearrangements in BALF cells has already been assessed in several studies. Thus, it was shown that PCR analysis of IGH rearrangements in patients with B-cell pulmonary lymphomas was sensitive (6 of 7 patients) and specific (0 of 9 control individuals) (12). Positive results were also obtained in 83% and 82% of patients with B-cell and MALT lymphomas at 90% and 97% specificity, respectively (13, 14). In the present study, we observed a similar sensitivity (88.9%) and specificity (90.0%) of IGH rearrangement detection for B-cell lymphoma diagnosis. We also analyzed TCR rearrangements using the TCRB clonal assay, which is considered one of the standard lymphoma diagnostic tools in Europe, detecting clonal TCRB rearrangements in 39.3–91.0% of T-cell lymphomas and in 3.8–16.0% of B-cell lymphomas (16–19). In the present study, TCR rearrangements were absent in BALF cells of patients with B-cell lymphomas but present in 33.3% and 13.3% of patients with LPD and other diseases, respectively. Unfortunately, we did not analyze patients with T-cell pulmonary lymphoma because of its rarity. Our results revealed that the presence of IGH rearrangements combined with the absence of TCR rearrangements had 96% specificity for the diagnosis of B-cell lymphoma. Unexpectedly, 75% of patients with MTX-related LPD exhibited clonal patterns (Supplementary Table S2), suggesting that TCR rearrangements may also be useful for diagnosing MTX-related LPD. Further studies are needed to evaluate the utility of TCR rearrangement testing in BALF cells for pulmonary T-cell lymphoma diagnosis.
Chromosomal translocations associated with MALT lymphoma include API2/MALT1, IGH/MALT1, BCL10/IGH, and trisomy 3 and 18 (14, 23, 27). The API2/MALT1 translocation was detected in 30–70% of MALT lymphoma lung tissues obtained by SLB (20, 21, 27–29), whereas the IGH/MALT1 translocation was revealed in 6–10% of patients with MALT lymphoma (27, 28). The probe for MALT1 translocation used in the present study detected both API2/MALT1 and IGH/MALT1 translocations, and the MALT1 translocation rate in patients with pulmonary MALT lymphomas observed here (28.6%) was consistent with previous reports (20, 21, 27–29). Owing to its 100% specificity, the FISH-based detection of MALT1 rearrangements in BALF cells would significantly improve the diagnostic accuracy for MALT lymphomas. Furthermore, the increased detection of genetic aberrations frequently observed in B-cell lymphomas, including BCL2, BCL6, IGH, and MALT1 translocations, should promote the development of lymphoma gene panels for BALF in the era of next-generation sequencing.
Besides clonality and gene translocation testing, phenotyping using various markers such as cluster of differentiation (CD) can be employed to diagnose lymphomas (30). For clonal analyses by PCR, the detection of rearrangements in heavy and light immunoglobulin chain genes (IGH, IGK, and IGL) and TCR genes (TCRB, TCRD, and TCRG) is a standard approach used in Europe to diagnose B- and T-cell lymphomas (16, 17, 19, 31); however, the combination of these gene rearrangements in BALF cells has not been analyzed. The detection of both IGH rearrangements and CD expression in BALF cells has been shown to aid in diagnosing pulmonary B-cell lymphoma: it revealed B-cell clonality as well as an increase in B-cell (CD19- or CD20-positive) lymphocytes to over 10% of total BALF lymphocytes (3, 12–14). Collectively, these data suggest that the combined analysis of disease markers such as clonality, gene translocations, and CD expression in BALF should aid in diagnosing pulmonary lymphomas through a less invasive method.