1. Hamartoma or fibrochondrolipoma is now considered to be a benign neoplasm. It is composed of myxoid mesenchymal tissue that undergoes maturation toward cartilage, mature fibrous tissue and fat. There are slit-like channels lined by bronchial epithelium which are incorporated into the lesion as it grows but are not an intrinsic component of the neoplasm.
2. Inflammatory pseudotumor is a non-neoplastic lesion composed of a variety of inflammatory cells (lymphocytes, plasma cells, histiocytes and most cells) and mesenchymal cells.

1. Adenocarcinoma is the most common lung cancer which usually arises from peripheral small bronchi and is often associated with a scar. The tumor cells form glands and secrete mucin. Mucus stains bright pink with mucicarmine stain and PAS after diastase. Bronchioloalveolar carcinoma (BAC) classically spreads in a single layer on top of alveolar septa that serve as scaffolding for the malignant cell growth. In half the tumors the cells are tall, well-differentiated, mucin-producing with basally located nuclei. Nonmucinous BAC is composed of tall columnar cells or cuboidal cells growing along the alveolar walls.
2. Squamous cell carcinoma, most strongly associated with smoking, can be well, moderately or poorly differentiated. The tumor cells are large, with pink cytoplasm and keratinization, forming keratin pearls. In the poorly differentiated carcinomas, the cells are highly atypical with rare individual cell keratinization.
3. Small cell carcinoma, regardless of histologic subtype, lacks a defined architectural pattern. It is composed of sheets of haphazardly arranged small cells with scantly cytoplasm. At low power, the tumor appears blue due to the closely opposed nuclei. There are numerous mitotic figures and foci of necrosis are present.

These(typical and atypical) are low-grade neuroendocrine carcinomas with organoid pattern and uniform cytologic features. The tumor cells are arranged in different patterns e.g., papillary, glandular, trabecular. The nuclei have finely granular chromatin (salt and pepper appearance). The atypical carcinoid has increased mitotic activity, more nuclear atypia and tumor necrosis.

3. Neuroendocrine carcinoma

1. Large cell neuroendocrine carcinoma is more pleomorphic than atypical carcinoid and has more mitoses and foci of necrosis.
2. Small cell neuroendocrine carcinomas are high grade small cell tumors with neuroendocrine features on immunohistochemistry and/or electron microscopy (these are a subtype of small cell carcinoma of lung).

These are typically rounded and multiple. The histology is usually the same as of the primary tumor.