A “tumor” is a swelling or lesion formed by the growth and division of tumor cells. “Tumor cells” are abnormal cells that divide in an uncontrolled manner and generally continue to divide after the stimuli that initiated growth and division ceases.
Tumors usually show partial or complete lack of structural organization and functional coordination with the normal tissue, and usually form a distinct mass of tissue, which may be either benign, pre-malignant, or malignant. For example, fibromas, also known as fibroid tumors or fibroids, are composed of fibrous or connective tissue and are usually benign tumors. Despite being benign, such tumors often require therapeutic intervention.
Cancer (medical term: malignant neoplasm) refers to a class of diseases in which a group of cells display uncontrolled growth (division beyond the normal limits), invasion (intrusion on and destruction of adjacent tissues), and sometimes metastasis. “Metastasis” refers to the spread of cancer cells from their original site of proliferation to another part of the body. For solid tumors, the formation of metastasis is a very complex process and depends on detachment of malignant cells from the primary tumor, invasion of the extracellular matrix, penetration of the endothelial basement membranes to enter the body cavity and vessels, and then, after being transported by the blood or lymph, infiltration of target organs. Finally, the growth of a new tumor, i.e. a secondary tumor or metastatic tumor, at the target site depends on angiogenesis. Tumor metastasis often occurs even after the removal of the primary tumor because tumor cells (including cancer stem cells) or components may remain and develop metastatic potential.
Cancerous solid tumors can be found, for example, in the bone, bladder, brain, breast, colon, esophagus, gastrointestinal tract, genito-urinary tract, kidney, liver, lung, nervous system, ovary, pancreas, prostate, retina, skin, stomach, testicles, and/or uterus.
Taking ovarian cancer as an example, this type of cancer is currently regarded as one of the most common cancer types among women. In 2012 alone, the number of new cases of ovarian cancer stood at 239,000, constituting 1.7% of all cancer cases worldwide, according to World Cancer Research Fund International.
Ovarian cancer is rarely diagnosed at its early stages, making the treatment of this cancer at an advanced stage difficult. Chemotherapy for ovarian cancer is most often a combination of 2 or more drugs, given IV every 3- to 4-weeks. Giving combinations of drugs rather than just one drug alone seems to be more effective in the initial treatment of ovarian cancer. The standard approach is the combination of a platinum compound, such as cisplatin or carboplatin, and a taxane, such as paclitaxel (Taxol®, Bristol-Myers Squibb, New York N.Y.) or docetaxel (commercially available as Taxotere®, Aventis Pharma, Antony, France). However, the use of chemotherapeutic agents across all cancer types suffers from two major limitations. First, chemotherapeutic agents are not specific for cancer cells and particularly at high doses, they are toxic to normal rapidly dividing cells. Second, with time and repeated use, cancer cells develop resistance to chemotherapeutic agents thereby providing no further benefit to the patient. Furthermore, as the survival rate among women suffering from ovarian cancer is poor, efforts are afoot to develop new medications and therapies for the effective treatment of this disease.