Mediastinal Germ Cell Tumor with Somatic-Type and Hematologic Malignancy
Borislav A. Alexiev, M.D.
Allen P. Burke, M.D.
Terminology
Germ cell tumor with somatic-type malignancy (GCT-STM) denotes a GCT containing a malignant somatic component of a type typically encountered in other organs or tissues, for example, carcinoma, sarcoma, and lymphoma/leukemia. A minimum size of one low-power field has been suggested as the threshold for the diagnosis of STM in GCTs. However, this size criterion is arbitrary. More important is the independent growth pattern demonstrated by the somatic-type malignancy.1
A unique type of somatic malignancy associated with mediastinal GCTs is that of hematologic malignancy, which, although not always within the mediastinal mass itself, is considered a manifestation of the GCT (Table 126.1).
Pathogenesis
The pathogenesis of GCT-STM is unknown. Divergent differentiation of a pluri- or totipotent primordial germ cell toward a GCT and the somatic-type malignancy has been suggested. This hypothesis is favored by the finding that “pure” mature mediastinal teratomas show no chromosome 12 abnormalities while a shared isochromosome 12p abnormality is characteristic of teratomas with somatic-type malignancies, including leukemias.2
Incidence and Clinical
GCT-STM has been classified into two clinical and pathologic types: GCT-STM induced by chemotherapy or irradiation3,4,5,6 and naturally occurring GCT-STM.7,8 The former type tends to occur in young patients (between 20 and 40 years of age) with an initial presentation of a mixed GCT.8,9,10,11 Naturally occurring teratoma-somatic-type malignancy is more frequently seen in older patients, with a peak incidence in the fifth and sixth decades of life.9
GCT-STM account for up to 29% of all mediastinal GCTs of adults but are almost nonexistent in children.2,6,8,11,12,13,14,15,16,17,18,19,20 The tumors occur predominantly in males.10 The somatic-type malignancy may arise in the primary mediastinal tumor or only in the metastases.1 The tumors show the same local symptoms as do other mediastinal GCTs, but they are more frequently symptomatic (˜90%) than pure GCTs.1 Tumor markers (α-fetoprotein, β-human chorionic gonadotropin, carcinoembryonic antigen) may be elevated according to the malignant components that are present.
Gross Pathology
GCT-STM usually exhibits a partially cystic and often variegated cut surface with focally necrotic areas. The carcinoma or sarcoma areas are firm and gray or hemorrhagic and often adherent to adjacent mediastinal structures.
TABLE 126.1 Characteristics of Somatic and Hematologic Malignancies Associated with Mediastinal GCTs | ||||||
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Microscopic Pathology
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