Malignant GCT.
Although GCTBs are usually benign, malignant GCTBs can be seen accounting for 1% - 2% of cases [19,26,27]. They differ clinically from the usual GCT, showing masses that grow fast with signs of local invasion and associated axillary adenopathy. They show higher rates of local recurrence [4,28,29]. The breast can also be secondarily involved with metastasis from primary malignant GCT elsewhere. Recurrence and metastasis, however, can occur with histologically benign or atypical GCTs [14,30]. When metastasis occurs, the most common sites are lungs and bones and less commonly liver, bowel, breast, thyroid, heart, pancreas, spleen, retroperitoneum, pharynx, mouth, neck, and brain [3]. There is no staging system for malignant GCTB [31].