Primary Solitary Mastocytoma of the Lung: A Case Report

Background Extracutaneous mastocytoma is really rare. Although only four cases of extracutaneous mastocytoma in lung have been reported in the literature to date, the cellular composition of mast cell tumors has not yet been conrmed. Here we report a new case of primary solitary mastocytoma and try to discuss its cellular composition. report: A 46-year-old woman, who has been having bronchial asthma for 3 years, had been found a nodules in the left lower lobe of lung by computed tomography (CT) scan because of chest pain, distress, and pain in the left thoracic region of the back for 10 days. Then the left inferior pulmonectomy and lymphadenectomy were performed. We conrmed the presence of mast cells in the resected tumor by immunohistology (i.e., strong CD117 and CD45 staining and positivity for tryptase) and toluidine blue staining. Additionally, our ndings suggested that solitary mast cell tumors was consisted of mature mast cells and immature mast cells with features of epithelial cells. A diagnosis of solitary mastocytoma of the lung was suggested. By now, the patient’s overall health was normal. No signs of recurrence was found. Symptoms of bronchial asthma were signicantly alleviated as well. further study. Although it can be detected in the lungs, lung ECM is very rare. [7] To the best of our knowledge, only four cases of lung ECM have been reported to date, including the rst case reported by Sherwin et al. in 1965. [8,9] In this study, we discuss a new case of solitary mastocytoma of the lung and its immunohistochemical ndings. Considering operative and relative drug therapy can release symptoms caused by mediators secreted by mast cells effectively, we expect our study will do some favor to diagnosis and treatment timely.

proportion of granular cells among the total cell population was approximately 15-30% at different locations in the tumor. No mitosis or atypia was observed. However, necrosis was found, and abundant capillaries and arterioles were detected throughout the lesion. No lymph node metastasis was observed.
Toluidine blue staining showed many purple heterochromatic particles in the cytoplasm of mast cells and a 1:2 ratio of mast cells to monocytes ( Fig. 2A).
According to immunohistochemistry results, mast cells showed positive staining for CD117 (Fig. 2B) and CD45, whereas monocytoid cells lacked immunoreactivity for these markers. Additionally, mast cells appeared positive for tryptase (strong positive staining in mast cells and weak positive staining in monocytoid cells; Fig. 2C). The percentage of strongly positive cells among the total cell population ranged from 30-60% at different locations in the tumor.
Considering the above ndings and the diagnostic criteria of the WHO classi cation for mastocytosis, [8] a diagnosis of solitary mastocytoma of the lung was suggested.
As of July 8, 2019, the patient overall health was normal, and subsequent imaging showed no signs of recurrence. In addition, symptoms of bronchial asthma were signi cantly alleviated after operation.

Discussion
ECM is a benign variant of mastocytosis. Although ECM is mainly detected in the lungs, lesions in the lungs are very rare. [1][2][3]7] According to the available literature, only four cases of ECM have been reported to date. The details of these cases and the current case are given in Table 1. [8][9][10][11]  staining of tryptase in monocytoid cells, we speculated that monocytes may be mast cells with few components. In our study, all neoplastic cells expressed CAM5.2, EMA, and β-catenin (cell membrane localization), and monocytoid cells also expressed TTF-1. We hypothesized that solitary mast cell tumors may be composed of mature and immature mast cells with features of epithelial cells. However, further research is necessary to con rm this hypothesis and explore the reason why tumor cells exhibited epithelial immunophenotype.
The conservative growth pattern and relatively low proportion of Ki-67 staining indicated the benign nature of the tumor in our case. This helped us to rule out mast cell sarcoma. In addition, according to a study by Valent et al. [7] and the WHO criteria for systemic mastocytosis and ECM, [7,13] lack of CD2 expression and no remarkable ndings in the skin or other systems provided us with clues and allowed us to exclude SM. Additionally, there were some morphological and immunohistochemical similarities of the current case with sclerosing pneumocytoma owing to the absence of papillary histology, sclerotic patterns, hemorrhage, glandular structure, and CK7 staining, excluding the existence of glandular epithelium. Thus, we reached a diagnosis of isolated mast cell tumors of the lung.
The patient in our case had asthma symptoms. We assumed that these symptoms may be caused by mediators of histamine, prostaglandin D2, cysteinyl leukotriene receptor, and platelet-activating factor released from mast cells. [7] The alleviation of symptoms after lobectomy may support this view.

Conclusion
In this report, we described Consent for publication: The written informed consent was obtained from the patient.
Availability of data and materials: The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
Competing interests: The authors declare that they have no competing interests Funding: none Authors' contributions: HW and YX performed the histological examination. HW was a major contributor in writing the manuscript. HFJ analyzed and interpreted the Histological and immunohistochemical results of the tumor and made the diagnosis. All authors read and approved the nal manuscript.
Acknowledgements: Not applicable