Methods of Classifying Cancers

Classifying by Type of Tissue

• Carcinoma: a neoplasm ("new growth") occurring in the epithelial cells that line organs and cover the surface of the body (~ 90% of all cancers fit into this category)
• Sarcoma: a solid tumor occurring in connective tissue, muscle, and bone (~ 2% of all cancers)
• Leukemia or lymphoma: a neoplasm occurring in the circulatory (leukemia) or lymphatic (lymphoma) systems (~ 8% of all cancers)

Classifying by Type of Cell Transformed

• Adenomatous cells —ductal or glandular cells
• Squamous cells —flat cells
• Myeloid —blood cell
• Lymphoid —lymphocytes or macrophages

Classifying by Site of Origin, Tissue or Cell Type, and/or Founder's Name

• Breast —breast carcinoma of ductal, medullary, papillary, etc, cells
• Bone —osteosarcoma, Ewing's sarcoma
• Eye —retinoblastoma
• Lip, tongue, mouth, nasal cavity —squamous cell carcinoma
• Lymphocytes —acute lymphocytic leukemia, chronic lymphocytic leukemia, Hodgkin's lymphoma
• Prostate —adenocarcinoma
• Ovary —adenocarcinoma, choriocarcinoma, teratoma, Brenner tumor

Cancers are Classified as Benign or Malignant:

• Benign tumors...
  • are generally slow growing and enclosed in a fibrous capsule
  • are generally considered innocuous, although their location can make surgical removal risky.
  • are not considered cancerous (that is, they are not malignant)
  • are given names that usually end in "oma" (although a melanoma is a malignant skin cancer)
• Malignant tumors...
  • proliferate rapidly, invading neighboring tissues
  • can metastasize, or spread, to other sites of the body
  • are named using the conventions of tissue, cell type, and origin
• Examples:
  • A tumor of the bone is an osteoma if benign and an osteosarcoma if malignant;
  • a tumor of nerve cells may be a ganglioneuroma if benign and a neuroblastoma if malignant;
  • a tumor of melanocytes are nevi if benign but a melanoma if malignant.

Classifying by Tumor Progression

The three variable TNM clinical staging system is used to describe the severity and extent of neoplasm progression.

• Tumor: size and appearance of the tumor. (TIS("in place"), T1, T2, and T3).
• Node: extent of lymph-node involvement. Metastasis is more likely with higher N numbers (N0, N1, N2, and N3).
• Metastasis: extent of metastases. M0 (metastases absent) or M1 (metastases present).