In approximately 22% of cases, malignant phyllodes tumours give rise to haematogenous metastases.4
The most frequent sites of metastases are the lungs, soft tissue, bone, and pleura.2,5
In most cases, the metastases resembles the sarcomatous component of the primary tumour.1,2
Our present case is very unusual in that only the metastatic lesions in the lungs revealed osteosarcomatous features, and there was no osteosarcomatous component in the primary tumour. One report described a local recurrence of a phyllodes tumour presenting with widespread differentiation into a teleangiectatic osteosarcoma, which was not apparent in the primary tumour.6
In that case, osteosarcomatous local recurrence occurred after the patient had undergone local but complete excision of a phyllodes tumour twice in the past. However, to our knowledge there are no reports that show osteosarcomatous differentiation only in a metastatic lesion of a phyllodes tumour. The reason why only the lung metastases revealed osteosarcomatous features is unclear; however, it is possible that there were undetectable small lesions differentiating into osteosarcoma in the primary breast tumour and that they had a high metastatic potential.
Take home messages
- To our knowledge, this is the first report of a phyllodes tumour with osteosarcomatous differentiation only in the metastatic lesions
- Careful follow up of this patient is necessary because the histological findings of both the primary and metastatic lesions include some factors associated with an unfavourable prognosis
Primary pulmonary osteosarcoma is extremely rare; to date, only 13 cases have been reported in the literature.7
Therefore, two primary osteosarcomas are not likely to occur simultaneously in the lungs. In addition, there was no evidence of other malignancies that might metastasise to the lungs. Thus, these two lung tumours were thought to be metastases from the malignant phyllodes tumour in the breast. It may be difficult to demonstrate directly by clonal studies that the lung tumours originate from the phyllodes tumour of the breast, because the genotype of the lung tumours may differ from that of the primary phyllodes tumour. Indeed, p53 immunoreactivity was seen only in the primary lesion and was absent from the lung tumours.
“It is possible that there were undetectable small lesions differentiating into osteosarcoma in the primary breast tumour and that they had a high metastatic potential”
Previous studies have attempted to define those histological features that would be useful in predicting the metastatic potential of a phyllodes tumour.1,2,4,5,8
Hawkins et al
showed that four features—high mitotic count, stromal overgrowth, severe nuclear pleomorphism, and infiltrating margins—were useful predictors for the development of metastases.2
They also showed that the most reliable predictor was the presence of stromal overgrowth. According to them, patients whose primary tumours contained areas of stromal overgrowth had a 72% risk of metastatic spread, whereas those without stromal overgrowth rarely had metastases. Therefore, for patients with unfavourable histological features, such as stromal overgrowth, it seems that a close follow up including chest CT and bone scintigram is necessary. Another study showed that phyllodes tumours with an osteosarcomatous component were potentially aggressive neoplasms, with distant metastasis and tumour related death occurring in 38% and 33% of patients, respectively.1
Moreover, the histological subtype of osteosarcoma in a phyllodes tumour was related to prognosis; the prognosis of osteoclastic and osteoblastic types was poorer than that of the fibroblastic type.1
In our present case, the lung metastases were diagnosed as osteoblastic type. Therefore, careful follow up is necessary because the histological findings of both the primary and metastatic lesions include some factors associated with an unfavourable prognosis.