1. Squamous cell carcinoma

A non-small cell carcinoma that on light microscopy (LM) exhibits intercellular bridges and/or keratinization

2. Small cell carcinoma (SCLC)

Small cell carcinoma (SCLC)

• a high grade carcinoma composed of small, often fusiform, cells with high N/C ratio
• poorly designed architecture with variable "organoid" growth
• usually extensive necrosis and high mitotic rate
• absent or inconspicuous nucleoli; finely granular ("salt and pepper") evenly dispersed chromatin
• nuclear moulding, DNA encrustation characteristic

3. Adenocarcinoma

A non-small cell carcinoma that exhibits either tubulo-acinar growth, papillary growth or mucin synthesis;

Bronchioloalveolar carcinoma is an adenocarcinoma which exhibits extension along airspace surfaces with little or no destruction of parenchymal architecture.

4. Large cell carcinoma

A non-small cell carcinoma with no LM evidence of differentiation (including negative mucin staining)

Large cell neuroendocrine carcinoma

• a high-grade carcinoma with LM neuroendocrine features such as "organoid" growth, palisading and rosette-like growth
• frequent necrosis and high mitotic rate (>10/10HPF)
• large cells, often polygonal rather than spindle form, low N/C ratio
• nucleoli usually evident, vesicular nuclear chromatin

5. Carcinoid Tumor

Typical carcinoid

• low grade NE tumor (IHC and/or EM+) composed of uniform cells of low N/C ratio
• no necrosis and rare mitoses
• nuclei feature small nucleoli, evenly dispersed fine chromatin
• cytoplasm appears finely granular

Atypical carcinoid

• a low grade NE tumor (IHC and/or EM+) which, on low-power LM, looks similar to carcinoid tumors, i.e. characterized by an "organoid" growth pattern
• nuclear pleomorphism, increased N/C ratio with areas of hypercellularity and disorganization of architecture
• focal micronecrosis; mitotic activity (2-10/10 HPF)
• cell nucleoli may be more prominent with coarser nuclear chromatin

6. Carcinomas of salivary gland type

Adenoid cystic carcinoma

• a low-grade carcinoma composed of epithelial and myoepithelial cells exhibiting tubuloacinar and/or cribriform (cylindromatous) differentiation with formation of myxoid and mucinous material
• usually central with an endobronchial polypoid component

Mucoepidermoid carcinoma

• usually a low-grade carcinoma composed of variable proportion of mucus-secreting cells, squamous cells (lack pearl/whorl formation) and cells of intermediate type
• usually central with an endobronchial polypoid component