This is the first reported case of a thymic carcinoid within a thymolipoma. Neuroendocrine tumours of the thymus are sometimes combined with different subtypes of thymomas and thymic carcinomas. In general, thymic carcinoid has a poor prognosis due to a high rate of recurrence and metastasis, but new therapeutic strategies including ocreotide based therapies may improve survival.4
Nevertheless, because of the rare occurrence of combined tumours of the thymus, data on therapy strategies and long-term follow-up are lacking.
Several combined thymoma tumours have been reported. Chen investigated a total of 200 thymomas1
and found several cases of mixed type thymomas (AB/B2, B2/B3 and B3/thymic carcinoma). In a large series of 228 patients reported by Ströbel et al
, 21% of cases showed combinations of type B1, B2 and B3 thymoma components and thymic carcinoma features in various proportions, with combinations of type B2 and B3 thymomas being by far the most common.5
Similar results were found in a study by Engel et al
Type A thymomas also seem to arise in combination with thymic carcinomas, but reported cases are rare.7–9
Perhaps some type A thymomas with spindle cell differentiation and type B3 features10
represent cases with tumour progression, however, these special cases of combined type A thymomas and thymic carcinomas need further investigation.
In the medical literature, only two cases of thymic tumours within a thymolipoma have been described. Recently, the occurrence of a type B2 thymoma and an undifferentiated thymic carcinoma within a thymolipoma arising in a 36-year-old woman has been reported.11
Another thymolipoma occurred in a 67-year-old, otherwise healthy female patient who was incidentally found to have an anterior mediastinal mass on radiographic examination. Microscopical examination showed an encapsulated type B thymoma within a thymolipoma.12
Additionally, thymic tumours can not only be associated with autoimmune disorders but also with leukaemias or lymphomas, especially T cell lymphomas.13
One case described by Khoury et al14
was composed of a type B thymoma and infiltrates of chronic lymphatic leukaemia, while another case reported by Pillai et al15
showed an association between a thymolipoma and classical Hodgkin lymphoma.
The question of whether combined tumours arise by different genetic pathways or whether, for example in cases of thymic carcinomas, a neuroendocrine component progresses via further genetic alterations into a neuroendocrine tumour, needs to be clarified. The latter possibility appears likely considering that thymic carcinomas often show scattered groups of neuroendocrine cells.4
In further support for such a mechanism Marx et al4
reported a case of combined B3 and large cell neuroendocrine carcinoma that shared a large number of genetic alterations.
In conclusion, when dealing with tumours of the thymus, one should always be aware of the possibility of combined tumours, the most frequent being mixed type thymomas.
- Combined tumours of the thymus are rare, the most frequent being mixed type thymomas.
- Symptoms of thymic carcinoid include chest pain, weight loss, cutaneous flushing, asthma-like symptoms and endocrinological disorders.
- Histological and immunohistochemical investigation of excised tumour specimens is required for confirmation of the diagnosis and successful treatment.