Sclerosing pneumocytoma is an uncommon, benign tumor that originates from the epithelial cells lining the lung’s air sacs. First identified in 1956, it was initially thought to be related to blood vessels, but further study revealed its origin from primitive respiratory cells known as type II pneumocytes. The name provides clues to its nature: “sclerosing” refers to the hardening of tissue seen under a microscope, and “pneumocytoma” indicates a tumor of the lung. This growth is classified as a type of lung adenoma, a non-cancerous tumor of glandular tissue.
Symptoms and Patient Demographics
Most individuals with a sclerosing pneumocytoma experience no symptoms, as a significant number of these tumors are found by chance during a chest scan for an unrelated issue. When symptoms do occur, they are non-specific and can include a persistent cough, shortness of breath, chest pain, or coughing up sputum, sometimes with blood. The presence of symptoms often depends on the tumor’s size and location within the lung.
The tumor is most frequently diagnosed in middle-aged women, with a peak incidence between the ages of 40 and 60. Studies show a strong female predominance, with female-to-male ratios reported as high as 14.5 to 1. There also appears to be a higher incidence among Asian women compared to Western populations. Unlike many other lung tumors, sclerosing pneumocytoma is not linked to a history of smoking; the vast majority of patients are non-smokers.
The Diagnostic Process
The diagnostic process begins with the discovery of a solitary pulmonary nodule on a chest X-ray or a computed tomography (CT) scan. On CT imaging, the tumor usually appears as a single, well-defined, and often oval-shaped mass. Radiologists may observe specific signs that suggest this tumor, such as a “halo sign” or an “overlying vessel sign,” though these are not present in all cases and are not definitive.
Further imaging with a positron emission tomography (PET) scan may be performed to assess the nodule’s metabolic activity. Sclerosing pneumocytomas can sometimes show increased metabolic activity, which can be mistaken for a malignant tumor. This overlap in imaging features means that imaging alone is often insufficient for a conclusive diagnosis, making a tissue sample necessary to distinguish it from lung cancer.
The definitive diagnosis is achieved through a biopsy, where a small piece of the tumor tissue is removed for examination. This can be done using a CT-guided fine-needle aspiration (FNA), a core needle biopsy, or a surgical biopsy like video-assisted thoracoscopic surgery (VATS). A pathologist then performs a histopathological examination, analyzing the tissue’s cellular structure under a microscope to confirm the diagnosis.
Pathology and Cellular Characteristics
Under the microscope, a sclerosing pneumocytoma has a distinct appearance characterized by two main types of cells: surface cuboidal cells and stromal round cells. Both of these cell types are thought to arise from a common progenitor cell but develop into different forms. Immunohistochemical staining is used to differentiate these cells and confirm their origin from lung epithelium.
These cells arrange themselves into four main growth patterns that can coexist in varying proportions within a single tumor.
- Papillary: Features finger-like projections.
- Sclerotic: Marked by dense, hardened connective tissue.
- Solid: Consists of dense sheets of the round stromal cells.
- Hemorrhagic: Characterized by blood-filled spaces, which contributed to its original name, “sclerosing hemangioma.”
Most tumors display at least two or three of these patterns.
Recent genetic research has identified a specific mutation in the AKT1 gene as a genetic hallmark of sclerosing pneumocytoma. This mutation is found in nearly all cases and is considered an event driving the tumor’s development. While this discovery helps confirm diagnoses on a molecular level, it currently has limited direct impact on patient treatment, as the standard approach remains surgical.
Treatment and Long-Term Prognosis
The standard and curative treatment for sclerosing pneumocytoma is complete surgical removal of the tumor. The specific surgical procedure chosen depends on factors like the tumor’s size and location. For smaller, peripherally located tumors, a sublobar resection is often performed, which includes either a wedge resection or a segmentectomy.
In cases where the tumor is larger or more centrally located, a lobectomy may be necessary, which involves the removal of an entire lobe of the lung. Minimally invasive techniques, such as video-assisted thoracoscopic surgery (VATS) or robotic-assisted surgery, are commonly used for these procedures. These approaches can lead to shorter hospital stays and faster recovery times.
Following complete surgical resection, the prognosis for patients is excellent. The tumor is considered benign, and recurrence is extremely rare. Metastasis, the spread of the tumor to other parts of the body, has been reported but is an exceptionally uncommon event. Because the surgery is curative, no further treatments like chemotherapy or radiation therapy are needed. Patients undergo follow-up imaging for a period after surgery to monitor for any signs of recurrence.