A 46-year-old woman had been experiencing chest pain, distress, and pain in the left thoracic region of the back for 10 days. The patient visited Laiyang Central Hospital on March 24, 2008. A computed tomography (CT) scan on the same day showed a lobular nodule in the size of 3.0 × 3.0 cm in the left lower lobe, exhibiting a spiculated pattern and uniform density. The patient denied having symptoms such as cough, expectoration, hemoptysis, fever, night sweat, hoarseness, and dysphagia and did not have a history of tuberculosis. However, the patient having bronchial asthma 3 years ago. No lesions were found on the skin, and complete blood counts demonstrated only the presence of acute inflammatory reaction. Liver and kidney function were normal. Except for right hepatic cysts measuring 1.2 × 1.1 cm, no obvious abnormalities were observed in ultrasound examination of the hepatobiliary tract, pancreas, or spleen.
According to these findings, left inferior pulmonectomy and lymphadenectomy were performed on March 30, 2008.
Specimens were fixed in 10% formalin and sliced. Tissue sections (4 µm thick) were stained with hematoxylin and eosin (H&E). A Roche autostainer, which uses the standard avidin/biotin/peroxidase complex technique, was applied for immunohistochemical studies. The primary antibodies included anti-CD117 (EP10), anti-CD45 (PD7/26 + 2B11), anti-thyroid transcription factor 1 (TTF-1; SPT24), anti-CAM5.2 (CAM5.2), anti-S-100 (4C4.9), anti-HMB45 (HMB45), anti-CD2 (UMAB6), anti-CD68 (KP1), anti-CD34 (UBEnD10), anti-actin (HHF35), and anti-Ki-67 and were purchased from Zhongshan (Beijing, China). Anti-mast cell tryptase (PB1058) was purchased from Boster (Beijing, China). Positive and negative controls were run simultaneously for all tested markers. All specimens were observed by two independent pathologists using an Olympus BX-43 microscope (Tokyo, Japan). Only clearly visible brown particles were categorized as positively stained.
A spherical, solid, fine texture nodule measuring 2.5 cm was found in the peripheral region of the left lower lobe of the lung. The nodule had clear boundaries with dark yellow to dark red cut surfaces. The remaining part of the left lower lobe was unremarkable (Fig. 1A). Furthermore, 10 lymphonodi were found.
The nodule was well circumscribed by a thin fibrous capsule and was composed of two types of cells. The first had a predominant lesion composition, polygonal mononuclear cell shape that was diffusely distributed in the nodules, and no clear boundaries between cells. These cells had clear or slightly eosinophilic cytoplasm and oval hypochromatic nuclei with coarse chromatin; small nucleoli were occasionally observed (Fig. 1B). The others were granular cells with deeply basophilic stained cytoplasm and relatively small hyperchromatic nuclei, which were scattered in the monocytoid cells (Fig. 1C, D). The 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. All cells were negative for cytokeratin 7 (CK7), S-100, HMB45, CD2, CD68, and actin; CD34 was only expressed in blood vessels, and CAM5.2, EMA, β-catenin (membrane localization), and vimentin were observed in all neoplastic cells (Fig. 2D-F). Finally, the proliferation index of Ki-67 was low (1–3%).
Considering the above findings and the diagnostic criteria of the WHO classification 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 significantly alleviated after operation.