Micronodular Thymic Carcinoma with Lymphoid Stroma: A Case Report.

Area of Science:

• Oncology
• Pathology
• Genetics

Background:

• Micronodular thymic carcinoma (MTC) with lymphoid hyperplasia is considered the malignant counterpart of micronodular thymoma (MT) with lymphoid hyperplasia.
• MTC shares morphological similarities with MT, suggesting a potential malignant transformation pathway.
• This report presents a unique case of MTC with lymphoid hyperplasia.

Observation:

• A 53-year-old woman presented with an incidentally discovered chest tumor.
• Histopathological examination revealed nodular epithelial nests with malignant morphology, including atypical cells and comedo necrosis, transitioning to low-grade thymoma-like areas.
• Immunohistochemistry showed expression of GLUT1, CD5, KIT, and BCL2 in carcinomatous elements, with attenuated expression in low-grade areas.

Findings:

• The tumor was negative for the *GTF2I* point mutation and Langerhans/dendritic cells, which are typically associated with favorable thymoma prognosis.
• The patient developed pleural metastasis 27 months postoperatively, necessitating treatment with lenvatinib.
• This case represents the first reported instance of a partially low-grade, *GTF2I*-negative MTC.

Implications:

• Histological and genetic findings in MTC may serve as prognostic indicators.
• Understanding the characteristics of this *GTF2I*-negative MTC could inform future diagnostic and therapeutic strategies.
• Further research into MTC subtypes and their genetic profiles is warranted to improve patient outcomes.