We identified two important clinical issues in the present case. Lung metastasis after radical resection of a primary lesion of a PEComa should be treated with complete surgical resection, if possible. In cases of multiple lung metastases requiring bilateral lobectomy, we recommend a safe two-step bilateral lobectomy.
First, lung metastasis after radical resection of a primary lesion of a PEComa should be treated with complete surgical resection, if possible. PEComa has malignant potential, and recurrence and distant metastases have been reported [2, 3]. Common metastatic sites are the liver, lymph nodes, lungs, and bone [2]. Although chemotherapy and mammalian target of rapamycin inhibitors have also been applied in a few cases, a standardized treatment strategy for lung metastasis of PEComas is not yet established [9]. At this time, surgical resection is considered the mainstay of treatment for resectable lung metastasis of PEComas [4,5,6,7]. Therefore, complete surgical resection for lung metastasis of PEComas is the appropriate treatment if conditions such as the general patient status and anatomical location of the metastasis permit.
Second, in cases of multiple lung metastases requiring bilateral lobectomy, we recommend a safe two-step approach. In general, if the predicted postoperative %FEV1 and % diffusing capacity for carbon monoxide values are both > 60%, the patient is considered at low risk of anatomic lung resection [10]. We considered bilateral lobectomy with a single step to confer rise of postoperative complication risk because the predicted postoperative %FEV1 was 56%. Thus, a two-step resection strategy was selected. First, left upper lobectomy of the larger lesion was performed. Three months later, we confirmed that the actual pulmonary function was better, the predicted postoperative %FEV1 was 63%, than the initial value and safely performed contralateral lobectomy. The postoperative pulmonary function was superior to the predicted values at any point in time. Takahashi et al. reported that never-smokers showed significantly greater compensatory response than smokers after major lung resection [11]. We believed that the factor of never-smoking related to the superior postoperative pulmonary function to the predicted values at both of times after first and second lung resections. We suggest that two-step resection strategy has the advantage of allowing gradual assessment of surgical tolerance. On the other hand, Toufektzian et al. reported that a pneumonectomy followed by contralateral lobectomy had high mortality rate, 33% [12]. We consider that a pneumonectomy combined with contralateral lobectomy should be avoided.
In this case, the histological feature and immunohistochemical staining results of the primary tumor of the colon and bilateral lung metastases were all consistent with the typical findings of PEComas. PEComas histologically comprise rounded or oval cells with abundant clear or eosinophilic cytoplasm and thin-walled sinusoidal vessels are characteristics [1]. PEComas stain most consistently for HMB-45, melan-A, and microphthalmia transcription factor and may also stain for S100 [1]. All tumors of this case were positive for HMB-45, caldesmon, and S100 and negative for desmin and α-smooth muscle actin. Although bilateral lung metastases were positive for melan-A, primary tumor of the colon had not been performed immunohistochemical staining for melan-A.
In addition, the time from initial radical resection of primary lesions of PEComas to recurrence or metastasis varies, and there remains no consensus on the duration of follow-up. Late recurrences have been reported up to 5 or 7 years after surgery [2, 4]. In the present case, the follow-up was completed up to 4 years after the initial surgery, and lung metastases were detected via a health examination 8 years postoperatively. Although the appropriate follow-up duration is a matter for future debate, we believe that a longer follow-up is desirable.
