Lymphocytes in thymomas are tolerant to self-MHC

Graft-versus-host disease-type colitis: an unusual association of malignant thymoma

We present the case of a patient with a malignant thymoma associated with a graft-versus-host disease-type colitis, of which there has only been a solitary case report in the world literature. Complete surgical resection of the thymoma was achieved; however, the gastrointestinal symptoms persisted.

Recurrent genetic aberrations in thymoma and thymic carcinoma

Apart from single reported aberrant karyotypes, genetic alterations in thymic epithelial neoplasms have not been investigated so far. In this study, 12 World Health Organization classification type A thymomas (medullary thymomas), 16 type B3 thymomas (well-differentiated thymic carcinomas), and nine type C thymomas, all of them primary thymic squamous cell carcinomas, were analyzed by comparative genomic hybridization and fluorescence in situ hybridization. With the exception of one single case, type A thymomas did not reveal chromosomal gains or losses in comparative genomic hybridization. In contrast, all type B3 thymomas showed chromosomal imbalances, with gain of 1q, loss of chromosome 6, and loss of 13q occurring in 11 (69%), six (38%), and five (31%) of 16 cases, respectively. In primary thymic squamous cell carcinoma, the most frequent chromosomal losses were observed for 16q (six of nine cases, 67%), 6 (4 of 9, 44%), and 3p and 17p (three of nine each, 33%), whereas recurrent gains of chromosomal material were gains of 1q (5 of 9, 56%), 17q, and 18 (three of nine each, 33%). This study shows that the distinct histological thymoma types A and B3 exhibit distinct genetic phenotypes, whereas type B3 thymoma and primary thymic squamous cell carcinoma partially share genetic aberrations. In addition to the possible tumorigenic role, the deletion in type B3 thymoma of chromosome 6, harboring the HLA locus, might play a role in the pathogenesis of paraneoplastic autoimmunity characteristic of thymoma.

Oligoclonal peripheral T-cell lymphocytosis as a result of aberrant T-cell development in a cortical thymoma

A 42-year-old man presented with a locally invasive cortical thymoma. Before chemotherapy was commenced 36 months after presentation, an unusual peripheral lymphocytosis of 19 x 10(9)/l had slowly developed over time. After the first course of chemotherapy, the lymphocytosis showed a sharp decline to normal absolute cell numbers and subsequently remained at normal levels. Currently, the patient is in stable partial remission and doing well. Immunophenotypic analysis showed a mature T-cell phenotype with 78% TcR-a beta and 16% TcR-gamma delta in the absence of an immature component. Pretreatment Southern blot analysis of peripheral blood mononuclear cells showed an oligoclonal pattern with 13-20 rearranged fragments of different intensity for the TcR beta-gene. TcR gamma also showed a pattern compatible with an oligoclonal proliferation. After treatment, after normalization of absolute blood counts, the distribution of T-cell subsets still showed a slightly aberrant pattern. Immunophenotypic analysis of a blood sample taken 6 months later, also at normal absolute cell counts, showed an increase of thymocytes as well as of mature T cells with a polyclonal pattern on Southern blot analysis. These findings may be interpreted as the result of aberrant positive and negative selection and development of thymocytes in the microenvironment of neoplastic thymic epithelial cells and clonal selection through continuous peripheral stimulation. Moreover, this case stresses the importance of integrated interpretation of clinical, morphological, immunophenotypical, and molecular data to gain insight in unusual clinical problems.

Delta-T-lymphocytosis in a patient with thymoma

BACKGROUND

Malignant thymoma is composed of neoplastic epithelial cells and small lymphocytes. Rarely, patients also may have peripheral T-lymphocytosis. These lymphocytes have been considered nonneoplastic because of their microscopic appearance and immunophenotype, as well as gene rearrangement studies.

METHODS

A 42-year-old man developed lymphocytosis 3 years after the completion of intensive combined chemoradiotherapy protocol for lymphocytic thymoma. These peripheral blood lymphocytes were evaluated phenotypically and genotypically.

RESULTS

Immunophenotyping established that the cells were CD3 positive, CD4 negative, CD8 negative, T-cell receptor (TCR)-alpha/beta negative, and TCR-gamma/delta positive. Gene rearrangement studies with TCR-delta probe confirmed the monoclonality of these cells. Chromosome analysis showed deletion of chromosome Y. The clinical course was progressive and had the features of malignant lymphoma.

CONCLUSIONS

To the authors' knowledge, this is the first report of a patient with thymoma in whom monoclonal proliferation of T-gamma/delta peripheral blood lymphocytes was confirmed immunophenotypically and genotypically. These monoclonal TCR-gamma/delta lymphocytes may belong to the malignant clone of the thymoma; however, the possibility that they represent an evolution of a second lymphatic malignancy cannot be excluded.