Some PanNETs do not cause any symptoms, in which case they may be discovered incidentally on a CT scan performed for a different purpose. Symptoms such as abdominal or back pain or pressure, diarrhea, indigestion, or yellowing of the skin and whites of the eyes can arise from the effects of a larger PanNET tumor, either locally or at a metastasis. About 40% of PanNETS have symptoms related to excessive secretion of hormones or active polypeptides and are accordingly labeled as "functional"; the symptoms reflect the type of hormone secreted, as discussed below. Up to 60% of PanNETs are nonsecretory or nonfunctional, in which there is no secretion, or the quantity or type of products, such as pancreatic polypeptide (PPoma), chromogranin A, and neurotensin, do not cause a clinical syndrome although blood levels may be elevated. In total, 85% of PanNETs have an elevated blood marker.

Functional tumors are often classified by the hormone most strongly secreted, for example:

- gastrinoma: the excessive gastrin causes Zollinger–Ellison syndrome (ZES) with peptic ulcers and diarrhea

- insulinoma: hypoglycemia occurs with concurrent elevations of insulin, proinsulin and C peptide

- glucagonoma: the symptoms are not all due to glucagon elevations, and include a rash, sore mouth, altered bowel habits, venous thrombosis, and high blood glucose levels

- VIPoma, producing excessive vasoactive intestinal peptide, which may cause profound chronic watery diarrhea and resultant dehydration, hypokalemia, and achlorhydria (WDHA or pancreatic cholera syndrome)

- somatostatinoma: these rare tumors are associated with elevated blood glucose levels, achlorhydria, cholelithiasis, and diarrhea

- less common types include ACTHoma, CRHoma, calcitoninoma, GHRHoma, GRFoma, and parathyroid hormone–related peptide tumor

In these various types of functional tumors, the frequency of malignancy and the survival prognosis have been estimated dissimilarly, but a pertinent accessible summary is available.

PanNETs are sometimes abbreviated as PETs or PNETs: such use should not to be confused with the primitive neuroectodermal tumor (PNET).

The majority of PanNETs are benign, while some are malignant. The World Health Organization (WHO) classification scheme places neuroendocrine tumors into three main categories, which emphasize the tumor grade rather than the anatomical origin. In practice, those tumors termed well or intermediately differentiated PanNETs in the WHO scheme are sometimes called "islet cell tumors." The high grade subtype, termed neuroendocrine cancer (NEC) in the WHO scheme, is synonymous with "islet cell carcinoma".

The World Health Organization (WHO) classification scheme places neuroendocrine tumors into three main categories, which emphasize the tumor grade rather than the anatomical origin:

- well-differentiated neuroendocrine tumours, further subdivided into tumors with benign and those with uncertain behavior

- well-differentiated (low grade) neuroendocrine carcinomas with low-grade malignant behavior

- poorly differentiated (high grade) neuroendocrine carcinomas, which are the large cell neuroendocrine and small cell carcinomas.

Additionally, the WHO scheme recognizes mixed tumors with both neuroendocrine and epithelial carcinoma features, such as goblet cell cancer, a rare gastrointestinal tract tumor.

Placing a given tumor into one of categories depends on well-defined histological features: size, lymphovascular invasion, mitotic counts, Ki-67 labelling index, invasion of adjacent organs, presence of metastases and whether they produce hormones.

Conceptually, there are two main types of NET within this category: those which arise from the gastrointestinal (GI) system and those that arise from the pancreas. In usage, the term "carcinoid" has often been applied to both, although sometimes it is restrictively applied to NETs of GI origin (as herein), or alternatively to those tumors which secrete functional hormones or polypeptides associated with clinical symptoms, as discussed.

The disease is more common in men than women and the average age at diagnosis is about 60.

Symptoms are often non-specific and include weight loss. A classic presentation, found in around 15% of cases includes subcutaneous nodules (due to fat necrosis) and arthralgias, caused by release of lipase.

A Hürthle cell () or Askanazy cell () is a cell in the thyroid that is often associated with Hashimoto's thyroiditis as well as benign and malignant tumors (Hürthle cell adenoma and Hürthle cell carcinoma, a subtype of follicular thyroid cancer). This version is a relatively rare form of differentiated thyroid cancer, accounting for only 3-10% of all differentiated thyroid cancers. Oncocytes in the thyroid are often called Hürthle cells. Although the terms oncocyte, oxyphilic cell, and Hürthle cell are used interchangeably, Hürthle cell is used only to indicate cells of thyroid follicular origin.

ACC are associated with increased serum lipase and manifest in the classic presentation as the "Schmid triad" (subcutaneous fat necrosis, polyarthritis, eosinophilia).

ACC are typically large, up to 10 cm, and soft compared to pancreatic adenocarcinoma, lacking its dense stroma. They can arise in any part of the pancreas.

Histomorphologically, the tumour resembles the cells of the pancreatic acini and, typically, have moderate granular cytoplasm that stain with both PAS and PASD.

Hürthle cell adenoma is the benign analogue of Hürthle cell carcinoma. This adenoma is extremely rare; when it occurs, it usually occurs in women. Often the adenoma is harmless but is removed after detection because its future course cannot be trusted. This mass can be detected and removed before transformation and metastasis. The tumor is often detected by imaging such as ultrasound. The location and size of the tumor may cause pressure and pain to the patient. But often the tumor goes undetected. After detection, the mass is tested using an invasive fine-needle aspiration biopsy.

The Hürthle cell is named after German histologist Karl Hürthle, who investigated thyroid secretory function, particularly in dogs. However, this is a misnomer since Hürthle actually described parafollicular C cells. The cell known as the Hürthle cell was first described in 1898 by Max Askanazy, who noted it in patients with Graves' disease.

Hürthle cell adenoma is a rare benign tumor, typically seen in women between the ages of 70 and 80 years old. This adenoma is characterized by a mass of benign Hürthle cells (Askanazy cells). Typically such a mass is removed because it is not easy to predict whether it will transform into the malignant counterpart, a subtype of follicular thyroid cancer called a Hürthle cell carcinoma.

Signet ring cell carcinoma (SRCC) is a rare form of highly malignant adenocarcinoma that produces mucin. It is an epithelial malignancy characterized by the histologic appearance of signet ring cells.

Primary SRCC tumors are most often found in the glandular cells of the stomach (SRCC originates in the stomach in 90 percent of patients), and less frequently in the breast, gallbladder, urinary bladder, and pancreas. SRCCs do not normally form in the lungs, though a few incidences have been reported.

Among colorectal cancers, the prevalence of SRCC is less than one percent. Though incidence and mortality of gastric cancer has declined in many countries over the past 50 years, there has been an increase in occurrences of gastric SRCC-type cancers.

SRCC tumors grow in characteristic sheets, which makes diagnosis using standard imaging techniques, like CT and PET scans, less effective.

Adenocarcinoma (; plural adenocarcinomas or adenocarcinomata ) is a type of cancerous tumor that can occur in several parts of the body. It is defined as neoplasia of epithelial tissue that has glandular origin, glandular characteristics, or both. Adenocarcinomas are part of the larger grouping of carcinomas, but are also sometimes called by more precise terms omitting the word, where these exist. Thus invasive ductal carcinoma, the most common form of breast cancer, is adenocarcinoma but does not use the term in its name—however, esophageal adenocarcinoma does to distinguish it from the other common type of esophageal cancer, esophageal squamous cell carcinoma. Several of the most common forms of cancer are adenocarcinomas, and the various sorts of adenocarcinoma vary greatly in all their aspects, so that few useful generalizations can be made about them.

In the most specific usage (narrowest sense), the glandular origin or traits are exocrine; endocrine gland tumors, such as a VIPoma, an insulinoma, or a pheochromocytoma, are typically not referred to as adenocarcinomas but rather are often called neuroendocrine tumors. Epithelial tissue sometimes includes, but is not limited to, the surface layer of skin, glands, and a variety of other tissue that lines the cavities and organs of the body. Epithelial tissue can be derived embryologically from any of the germ layers (ectoderm, endoderm, or mesoderm). To be classified as adenocarcinoma, the cells do not necessarily need to be part of a gland, as long as they have secretory properties. Adenocarcinoma is the malignant counterpart to adenoma, which is the benign form of such tumors. Sometimes adenomas transform into adenocarcinomas, but most do not.

Well differentiated adenocarcinomas tend to resemble the glandular tissue that they are derived from, while poorly differentiated adenocarcinomas may not. By staining the cells from a biopsy, a pathologist can determine whether the tumor is an adenocarcinoma or some other type of cancer. Adenocarcinomas can arise in many tissues of the body owing to the ubiquitous nature of glands within the body, and, more fundamentally, to the potency of epithelial cells. While each gland may not be secreting the same substance, as long as there is an exocrine function to the cell, it is considered glandular and its malignant form is therefore named adenocarcinoma.

Acinic cell carcinoma is a malignant tumor representing 2% of all salivary tumors. 90% of the time found in the parotid gland, 10% intraorally on buccal mucosa or palate. The disease presents as a slow growing mass, associated with pain or tenderness in 50% of the cases. Often appears pseudoencapsulated.

Basophilic, bland cells similar to acinar cells. Growth pattern: solid - acinar cells, microcytic - small systic spaces mucinous or eosinophilic, papillary-cystic - large cystic lined by epithelium, follicular - similar to thyroid tissue.

These tumors which resemble serous acinar cells vary in their behavior from locally aggressive to blatantly malignant.

It can also appear in the breast. The pancreatic form of acinic cell carcinoma is a rare subtype of exocrine pancreatic cancer. Exocrine pancreatic cancers are the most common form of pancreatic cancer when compared to endocrine pancreatic cancer.

Acinic cell carcinomas arise most frequently in the parotid gland. Other sites of primary tumors have included the submandibular gland and other major and minor salivary glands. There have been rare cases of primary tumors involving the parapharyngeal space and the sublingual gland.

Surface epithelial-stromal tumors are a class of ovarian neoplasms that may be benign or malignant. Neoplasms in this group are thought to be derived from the ovarian surface epithelium (modified peritoneum) or from endometrial or Fallopian tube (tubal) tissue. Tumors of this type are also called ovarian adenocarcinoma. This group of tumors accounts for 90% to 95% of all cases of ovarian cancer. Serum CA-125 is often elevated but is only 50% accurate so it is not a useful tumor marker to assess the progress of treatment.

Epithelial-stromal tumors are classified on the basis of the epithelial cell type, the relative amounts of epithelium and stroma, the presence of processes, and the location of the epithelial elements. Microscopic pathological features determine whether a surface epithelial-stromal tumor is benign, borderline, or malignant (evidence of malignancy and stromal invasion). Borderline tumors are of uncertain malignant potential.

This group consists of serous, mucinous, endometrioid, clear cell, and brenner (transitional cell) tumors, though there are a few mixed, undifferentiated and unclassified types.

This particular variant of lung cancer is usually asymptomatic and is found after chest x-rays are taken for other reasons. Hemoptysis is seen occasionally and, in some cases, distal obstruction of bronchi by blood clots or mucus plugs produces cough and/or infection. Lesions often enlarge and progress slowly, over many years.

The 1999 World Health Organization classification system defined MCACL as a cystic adenocarcinoma with copious mucin production that, histologically, resembles (the more common) mucus-producing cystadenocarcinomas originating in the ovary, breast and pancreas. The 2004 revision of the WHO classification noted that the tumors tend to be well circumscribed by a partial fibrous tissue capsule with central cystic change and copious mucin pooling. The thin, fibrous wall circumscribing the tumor is highly characteristic of this lesion. It can sometimes occur within a pulmonary bronchocele, and this tumor entity should be kept in mind after identification of a bronchocele with suspicious or non-prototypical imaging characteristics.

Microscopically, the neoplastic epithelial cells tend to grow along the alveolar walls, in a fashion similar to the mucinous variant of bronchioloalveolar carcinoma, a more common form of adenocarcinoma.

Hemoptysis is seen occasionally.

Positron Emission Tomography (PET) scanning can be of assistance in diagnosing MCACL, as these lesions show intense uptake, typically in the wall of the tumor.

CA 19-9 has been reported to be elevated in MCACL.

Differential diagnosis of MCACL includes secondary metastatic cystadenocarcinomatous lesions, particularly from the pancreas or ovary, mucoepidermoid carcinoma, and pulmonary mucinous bronchioloalveolar carcinoma. The mouse monoclonal antibody 1D3, developed to detect a high molecular weight mucin found in a number of cystic malignancies of various organs, may be of use in differentiating primary mucinous cystadenocarcinoma of the lung from metastatic lung tumors due to mucinous cystic lesions of the uterus and pancreas, as well as those primary in the colon and stomach.

Several other terms for this lesion have been used in the past medical literature, including mucinous multilocular cyst carcinoma, pseudomyxomatous pulmonary adenocarcinoma, mucinous cystic tumor of low malignant potential, and others.

Salivary gland–like carcinomas of the lung generally refers a class of rare cancers that arise from the uncontrolled cell division (mitosis) of mutated cancer stem cells in lung tissue. They take their name partly from the appearance of their abnormal cells, whose structure and features closely resemble those of cancers that form in the major salivary glands (parotid glands, submandibular glands and sublingual glands) of the head and neck. Carcinoma is a term for malignant neoplasms derived from cells of epithelial lineage, and/or that exhibit cytological or tissue architectural features characteristically found in epithelial cells.

This class of primary lung cancers contains several histological variants, including mucoepidermoid carcinoma of the lung, adenoid cystic carcinoma of the lung, epithelial-myoepithelial carcinoma of the lung, and other (even more rare) variants. .

Due to the diverse nature of salivary gland tumours, many different terms and classification systems have been used. Perhaps the most widely used currently is that system proposed by the World Health Organization in 2004, which classifies salivary neoplasms as primary or secondary, benign or malignant, and also by tissue of origin. This system defines five broad categories of salivary gland neoplasms:

Benign epithelial tumors

- Pleomorphic adenoma

- Warthin's tumor

- Myoepithelioma

- Basal cell adenoma

- Oncocytoma

- Canalicular adenoma

- Lymphadenoma

- "Sebaceous lymphadenoma"

- "Nonsebaceous lymphadenoma"

- Ductal papilloma

- "Inverted ductal papilloma"

- "Intraductal papilloma"

- "Sialadenoma papilliferum"

- Cystadenoma

- Malignant epithelial tumors

- Acinic cell carcinoma

- Mucoepidermoid carcinoma

- Adenoid cystic carcinoma

- Polymorphous low-grade adenocarcinoma

- Epithelial-myoepithelial carcinoma

- Clear cell carcinoma, not otherwise specified

- Basal cell adenocarcinoma

- Sebaceous carcinoma

- Sebaceous lymphadenocarcinoma

- Cystadenocarcinoma

- Low-grade cribriform cystadenocarcinoma

- Mucinous adenocarcinoma

- Oncocytic carcinoma

- Salivary duct carcinoma

- Salivary duct carcinoma, not otherwise specified

- Adenocarcinoma, not otherwise specified

- Myoepithelial carcinoma

- Carcinoma ex pleomorphic adenoma

- Mammary analogue secretory carcinoma

- Carcinosarcoma

- Metastasizing pleomorphic adenoma

- Squamous cell carcinoma

- Large cell carcinoma

- Lymphoepithelial carcinoma

- Sialoblastoma

- Soft tissue tumors

- Hemangioma

- Hematolymphoid tumors

- Hodgkin lymphoma

- Diffuse large B-cell lymphoma

- Extranodal marginal zone B cell lymphoma

- Secondary tumors (i.e. a tumor which has metastasized to the salivary gland from a distant location)

Others, not included in the WHO classification above, include:

- Intraosseous (central) salivary gland tumors

- Hybrid tumors (i.e. a tumor displaying combined forms of histologic tumor types)

- Hybrid carcinoma

- Others

- Others

- Keratocystoma

- Sialolipoma

Patients typically present with a non-productive cough and weight loss.

Carcinoma is a type of cancer that develops from epithelial cells. Specifically, a carcinoma is a cancer that begins in a tissue that lines the inner or outer surfaces of the body, and that arises from cells originating in the endodermal, mesodermal and ectodermal germ layer during embryogenesis.

Carcinomas occur when the DNA of a cell is damaged or altered and the cell begins to grow uncontrollably and become malignant. It is from the Greek καρκίνωμα 'karkinoma' meaning sore, ulcer, or cancer, itself derived from "karkinos" 'crab'.

Combined small cell lung carcinoma (or c-SCLC, and rarely rendered as "small-cell lung carcinoma") is a form of multiphasic lung cancer that is diagnosed by a pathologist when a malignant tumor arising from transformed cells originating in lung tissue contains a component of small cell lung carcinoma (SCLC) admixed with one (or more) components of non-small cell lung carcinoma (NSCLC).

It is impossible to distinguish between follicular adenoma and carcinoma on cytological grounds. If fine needle aspiration cytology (FNAC) suggests follicular neoplasm, thyroid lobectomy should be performed to establish the histopathological diagnosis. Features "sine qua non" for the diagnosis of follicular carcinoma are capsular invasion and vascular invasion by tumor cells. Still, focuses of the capsular invasion should be carefully evaluated and discriminated from the capsular rupture due to FNA penetration resulting in WHAFFT ("worrisome histologic alterations following FNA of thyroid").

- Follicular carcinoma tends to metastasize to lung and bone via the bloodstream.

- Papillary thyroid carcinoma commonly metastasizes to cervical lymph nodes.

HMGA2 has been proposed as a marker to identify malignant tumors.

Lung cancer is a large and exceptionally heterogeneous family of malignancies. Over 50 different histological variants are explicitly recognized within the 2004 revision of the World Health Organization (WHO) typing system ("WHO-2004"), currently the most widely used lung cancer classification scheme. Many of these entities are rare, recently described, and poorly understood. However, since different forms of malignant tumors generally exhibit diverse genetic, biological, and clinical properties — including response to treatment — accurate classification of lung cancer cases are critical to assuring that patients with lung cancer receive optimum management.

Under WHO-2004, lung carcinomas are divided into 8 major taxa:

- Squamous cell carcinoma

- Small cell carcinoma

- Adenocarcinoma

- Large cell carcinoma

- Adenosquamous carcinoma

- Sarcomatoid carcinoma

- Carcinoid tumor

- Salivary gland-like carcinoma