myoepithelial carcinoma ( mc ) is a rare tumor with an incidence of 0.2% of all salivary gland tumors . most of the reported cases of mc arise in the parotid gland ( 4875% ) , followed by minor salivary glands , and the submandibular gland .
the first case was described by higashiyama et al . , in 1998 . since then , only seven cases have been reported in literature .
a mentally retarded 13-year - old girl , with a history of congenital hypothyroidism and cystic lymphangioma in the left dorsal region , operated in 2004 , had consulted for cough and dyspnea in september 2010 .
physical examination showed a decrease in vesicular breath sounds at the basal areas of chest bilaterally , without fever .
pulmonary computed tomography ( ct ) showed bilateral pleural masses measuring 6.3 cm and 7.4 cm at the right and left bases , respectively , with lymph node metastases [ figure 2 ] .
( a ) bilateral pulmonary opacities ( b ) disappearance of pulmonary opacities pulmonary computed tomography ( ct ) : bilateral pulmonary masses a histopathological study of the left pleural biopsy revealed a monomorphic proliferation of round cells with clear cytoplasm and a weak , mitotic hyperchromatic oval nucleus [ figure 3 ] .
there were some cohesive layers , separated by bands of sclerosis ; the stroma was sparse with foci of necrosis .
the immunohistochemistry ( ihc ) study was focally positive for vimentin , cd99 , and ps100 .
the abdominal ultrasound , bone scan , and metaiodobenzylguanidine ( mibg ) scintigraphy were normal .
the histopathological and the ihc review at the  institut bergoni  in france concluded the diagnosis of myoepithelial carcinoma of the soft tissues with intermediate malignancy .
ihc was positive for pancytokeratin ( ae1/ae3 ) and ps100 , and negative for ema , cd34 , desmin , and cd99 .
the progression was marked by the disappearance of the pulmonary opacities [ figure 1 ] .
they include mucoepidermoid carcinoma , adenoid cystic carcinoma , acinic cell carcinoma , oncocytoma , epithelial 
it arises from the submucosal bronchial glands of the lower respiratory tract . in the world health organization classification , published in 2004 ,
mc was cited as being synonymous with epithelial  myoepithelial carcinoma . as mc and epithelial 
myoepithelial carcinoma of the salivary gland are distinguished by the presence or absence of ductal cells , their pulmonary counterparts must also be differentiated .
myoepithelial tumors are low - grade lesions without recurrences or metastasis described after resection , whereas , the rate of metastasis in mc is high , as seen in our case .
our patient represents the first pediatric case , described in the literature , having primitive pulmonary mc .
the tumor was peripheral and bilateral , measuring 6 cm and 7 cm , which was in agreement with the literature .
in fact , the size of the mc ranged from 15 mm to 130 mm ( mean 50.7 mm ) [ table 1 ] . characteristics of pulmonary mc in our case , the histopathological study oriented to the diagnosis of a primitive neuroectodermal tumor or neuroblastoma .
the pathological review , with further ihc analysis in france , had concluded the diagnosis of mc .
the following markers were found to be useful in myoepithelial carcinoma : cytokeratins ( ae1/ae3 ) and vimentin ( reported to be positive in neoplastic myoepithelial cells and negative in normal myoepithelial cells ) .
other variable markers , such as , ps100 , calponin , smooth muscle actin ( sma ) , muscle - specific actin ( msa ) , smooth muscle myosin , and p63 protein , could be positive .
however , neoplastic transformation of myoepithelial cells could result in a loss or a modification of their smooth muscle phenotype . in our case ,
although the eight patients reported in literature were treated with optimal surgery , metastases were reported in seven of them ( 87.5% ) ( contralateral lung , forearm , liver , and brain ) .
it was significant that a patient who had not developed metastasis , had the lowest tumor mitotic rate of 5/10 hpfs .
this fact reasoned that the mitotic rate could be an important prognostic factor of the clinical outcome and survival in primary myoepithelial carcinoma of the lung .
given the rarity of these tumors , recommendations regarding chemotherapy or radiation , either pre- or postoperatively , are difficult to formulate .
the originality of our case is the disappearance of the pulmonary opacity spontaneously , without any treatment .
our case represents , to the best of our knowledge , the first pediatric case having primitive pulmonary mc .
the histopathological study familiarizes the diagnosis , but a further ihc study is needed to confirm the diagnosis and to eliminate other etiologies .
surgery represents the main treatment for the operable forms . to the best of our knowledge ,
we have reported the first case , with spontaneous regression of this tumor , without any treatment .
 primary myoepithelial carcinoma ( mc ) of the lung is exceedingly rare . 
 we report here , to the best of our knowledge , the first pediatric case having primitive pulmonary mc . 
 the originality of our case was the disappearance of the pulmonary opacity spontaneously , without any treatment . 
 the difficulties in our case were the diagnosis of this rare entity and its subsequent treatment . 
 in fact , given the rarity of these tumors , recommendations regarding chemotherapy or radiation , were difficult to formulate . 