of the lung is a distinct type of adenocarcinoma with complex
This unusual histopathological growth pattern is characterized by complex papillary infoldings.
In most cases, areas of adenocarcinoma can be identified.
Pure form need to be distinguished from other types of tumours (Example: Ovary or Thyroid Gland).
Papillary carcinoma of the lung is composed of papillary tufts containing fibrovascular cores.
Psammoma bodies can also be seen.
Necrosis is often present in the lumens of the alveoli.
Electron microscopy revealed the tumour cells to possess the lamellated intracytoplasmic inclusions characteristic of normal and neoplastic type II pneumocytes.
Differential diagnosis: Pure papillary carcinomas of the lung can show histopathologic features similar to those seen in the ovary or thyroid gland. Thus, a detailed clinical history is of importance.
1. The tumour may mimic a papillary thyroid carcinoma - thyroglobulin stain should help in the differential diagnosis.
2. Separation from metastatic papillary carcinoma of ovarian origin requires a detailed clinical history, pelvic examination, and radiologic studies to allow adequate identification of the latter.
More recently, a variant of this tumour closely resembling similar tumours in the urinary bladder has been described as micropapillary carcinoma.
A micropapillary pattern (MPP) in lung adenocarcinoma, characterized by papillary structures with epithelial tufts lacking a central fibrovascular core, has been reported to be a new pathological marker of poor prognosis.
Micropapillary differentiation in adenocarcinomas has recently been associated with poor prognosis because these tumors are more likely to metastasize. However, no clear explanation exists as to why the presence of a micropapillary pattern is associated with metastasis.
The immunohistochemical profile may be helpful in determining the primary location of the neoplasm containing micropapillary features.
Myofibroblasts are present in the stroma of the invasive neoplastic nests in the micropapillary component as well as the conventional adenocarcinoma component, and D2-40 monoclonal antibody may be useful for evaluating the lymphatic invasion of pulmonary micropapillary carcinoma.
Papillary Carcinoma With Prominent "Morular" Component:
This recently described tumour is a morphologic variant of "true" papillary carcinoma of the lung.
This unusual variant is distinguished by the presence of cell aggregates that form squamoid "morules," similar to those observed in Pulmonary Blastoma.
Differential diagnosis: Papillary structures with high nuclear grade will favor a diagnosis of morular papillary carcinoma. Presence of cribriform glandular structures lined by clear cells will support a diagnosis of pulmonary blastoma.
Micropapillary pattern: a distinct pathological marker to subclassify tumours with a significantly poor prognosis within small peripheral lung adenocarcinoma (</=20 mm) with mixed bronchioloalveolar and invasive subtypes (Noguchi's type C tumours).
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