OVERVIEW

• The basic components of a tumor are the parenchyma and stroma.
  — The parenchyma comprises the neoplastic cells.
  — The stroma comprises the supporting connective tissues, blood vessels, and immune cells.
• Interactions between these components determine the growth and behaviors of the neoplasm.
• Benign tumors are localized, organized, and tend to display slower growth.
  — Because of these characteristics, benign tumors are typically amenable to surgical removal, which may be necessary when benign tumors grow large enough to impair functioning of the surrounding tissues.
• Malignant tumors are invasive, disorganized, and often grow erratically; they are potentially metastatic, which means they can cross anatomical boundaries.

BENIGN

• Benign tumors are often named by combing the cell type of origin with the suffix “-oma;” however, some important exception to this rule are the malignant tumors of lymphoma, mesothelioma, and melanoma.

Adenoma of the thyroid gland

• Well differentiated, which means that the tumor cells resemble that of the normal thyroid gland.
• It is functional, as we can see numerous colloid-filled follicles.
• Relatively normal looking nuclei.

Pancreatic tissue with serous cystadenomas

• Microcysts
• The pancreatic acini are relatively normal looking.
• Serous cystadenomas are also often commonly found in the ovaries.

Squamous papillomas on the tongue

• Numerous macroscopic fingerlike and warty projections.
• When such projections extend into a lumen, they are called “polyps.”

MALIGNANT

• Sarcomas are malignant tumors that form in sold mesenchymal tissue, such as bone, fat, and muscle.
• Leukemias and lymphomas are cancers of the white blood cell lines.
• Carcinomas are tumors that form from epithelial cells, such as in the skin or the internal linings of the organs.
  — Squamous cell carcinomas: the tumor cells look like stratified squamous epithelium, and,
  — Adenocarcinomas: the tumor cells grow in a glandular pattern.
• “Undifferentiated malignant tumors” are those of unknown tissue origins.

Adenocarcinoma in the colon

• It is anaplastic, that its, it is not well differentiated. The glandular tissue that has proliferated is not like that of the normal colon mucosa.
• See image of a large polyp growing from the wall of the colon; even if this wasn’t a malignant tumor, we can see how this would obstruct normal bowel functioning.

Oral squamous cell carcinoma

• Pleiomorphic cells, which range from small to giant.
• Large, hyperchromatic nuclei.
• Several of the cells are in various stages of mitosis, reflective of their hyper-proliferative state.

Thyroid adenocarcinoma

• The malignant tumor is anaplastic and disorganized.
• It is nonfunctional, which we can see from the absence of colloid-filled follicles.

Metastatic brain tumor

• It has irregular edges without a distinct enclosing capsule, which lends to its invasive nature.

Some special cases

• Mixed tumors
  The parenchymal cells of most tumors are uniform; however, denote that mixed tumors comprise multiple cell types.
  For example, a mixed tumor of the salivary gland may comprise epithelial cells as well as other types not typically found in the gland.
• Teratomas
  The cells of most neoplasms are derived from a single germ cell layer; however, denote that teratomas comprise cells and tissues from multiple germ layers.
  For example, we can see multiple tissue types in an ovarian teratoma, even hair and tooth-like structures.