Micronodular thymoma with lymphoid stroma diagnosed 10 years after the first operation: a case report

GTF2I mutation in micronodular thymoma with lymphoid stroma

AIMS

Micronodular thymoma with lymphoid stroma is a rare subtype of thymoma with characteristic clinical and pathological features. Some of the features, such as indolent nature, principally spindle morphology and no significant association to myasthenia gravis, are shared with type A and AB thymoma, which is closely linked to GTF2I mutation. However, not much is known regarding the molecular genetics of this thymoma subtype. In this study, the GTF2I mutation status was investigated in 16 cases of micronodular thymoma.

METHODS

16 micronodular thymomas were retrieved and the GTF2I mutation was tested by Sanger sequencing. The clinicopathological findings were documented.

RESULTS

GTF2I c.1271T>A p.(Leu424His) mutation within exon 15 was detected in 14 out of 16 tumours (87.5%). Two patients died of other causes while all others remained alive with no evidence of recurrence during the follow-up period ranging from 19 to 188 months (median: 100 months).

CONCLUSIONS

GTF2I mutation status and presence of spindle cell morphology may indicate that type A and AB thymoma, and micronodular thymoma represent a group biologically distinct from type B thymomas, which generally lack this mutation.

Comparative clinicopathological and immunohistochemical study of micronodular thymoma and micronodular thymic carcinoma with lymphoid stroma

AIM

To elucidate the clinicopathological and immunohistochemical characteristics of micronodular thymomas (MNTs) and micronodular thymic carcinomas (MNCs) with lymphoid stroma.

METHODS

We examined four cases of MNTs and three cases of MNCs pathologically and immunohistochemically.

RESULTS

There were prominent cystic changes infive of the seven cases. The neoplasms contained epithelial tumour cells arranged in a micronodular growth pattern lined by cystic walls and separated by abundant lymphoid stroma. Only the tumour cell component of MNCs showed signs of malignancy characterised by cytological atypia and increased mitotic activity. Neoplastic MNC epithelial cells showed strong positivity for CD5 and CD117. However, no immature lymphocytes (TdT-positive and CD99-positive) were present in and around the tumour nodules. None of the patients died or suffered from disease due to MNTs or MNCs.

CONCLUSION

MNTs and MNCs are rare and less aggressive forms of thymic tumours and can be differentially diagnosed by immunohistochemistry.

Difference in the distribution of tumor-infiltrating CD8+ T cells and FOXP3+ T cells between micronodular thymoma with lymphoid stroma and micronodular thymic carcinoma with lymphoid stroma

Micronodular thymoma with lymphoid stroma (MNT) is a rare thymic epithelial neoplasm subtype characterized by a micronodular tumor cell growth pattern and abundant lymphoid stroma. Micronodular thymic carcinoma with lymphoid stroma (MNCA) is considered as a malignant counterpart of MNT and exhibits a growth pattern similar to that of MNT but has histologic features reminiscent of thymic squamous cell carcinoma, such as cytologic atypia and CD5 and CD117 immunoexpression. Although both MNT and MNCA are characterized by abundant lymphoid stroma, it remains unknown whether there are differences in infiltrating lymphocytes between MNT and MNCA. We analyzed the immune microenvironment profile in eight MNT and three MNCA cases. The cell density of CD8‐positive T cells was significantly higher in MNT than in MNCA, whereas that of FOXP3‐positive T cells was significantly higher in MNCA than in MNT. There was no significant difference in the cell density of programmed death protein 1‐positive T cells and programmed death ligand 1 expression between the MNT and MNCA cases. Our findings indicated that the immune microenvironment of MNCA differed from that of MNT and, compared with the T‐cell profile of MNT, that of MNCA was more suppressive to patients′ antitumor immune response.

Surgical treatment of micronodular thymoma with lymphoid stroma

This case was about a 71‐year‐old man presented to our clinic for an anterior mediastinal mass found on routine chest computed tomography (CT). CT scan showed a lobulating contoured mass in the anterior mediastinum. A preliminary diagnosis was thymoma. The patient underwent subxiphoid uniportal video‐assisted thoracoscopic surgery for the extended thymectomy and complete excision of the tumour. The pathological examination showed a micronodular thymoma with lymphoid stroma (MTWLS). In conclusion, this report described an extremely rare tumour, MTWLS, and MTWLS might be considered in the differential diagnosis of mediastinal tumour, especially thymoma.