CD138 (Syndecan-1) in thymic tumors: correlation with various World Health Organization types and clinical outcome

We intended to explore the relationship of CD138 with thymic tumors. A series of 64 thymic tumors were studied. Positive staining was seen in 7 of 8 (87.5%) type A, 7 of 16 (43.7%) type AB, 1 of 8 (12.5%) type B1, 1 of 5 (20%) type B2, 10 of 17 (58.8%) type B3, and 3 of 10 (30%) type C (p=0.04), respectively. In terms of subcellular location of CD138 expression, 9 of 10 (90%) CD138 positive type B3 had membranous expression, while cytoplasmic expression was identified in 7 of 7 (100%) type A, and 6 of 7 (86%) type AB (p<0.0001). Positive CD138 was noted in 20 of 31 (64.5%) cases with Masaoka stage I (p= 0.01); while negative CD138 was seen in 24 of 33 (72.7%) cases with Masaoka stages (II-IV). Tumor recurred in 4 cases (7%), all of which had negative CD138 (p=0.008). Our study suggests that CD138 could be used as an ancillary study to differentiate between WHO types. Furthermore, our findings demonstrate that advanced stage-thymic tumors as well as those with high recurrence rate tend to display a reduced expression of CD138. However, more studies with larger cohort and longer follow-up are warranted to validate the clinical utility of CD138 to assess clinical behavior and prognosis of thymic tumors.