Cancer is the second leading cause of death worldwide. Although great advancements have been made in the treatment and control of cancer progression, significant deficiencies and room for improvement remain. A number of undesired side effects sometimes occur during chemotherapy. Natural therapies, such as the use of plant-derived products in cancer treatment, may reduce adverse side effects. Currently, a few plant products are being used to treat cancer. However, a myriad of many plant products exist that have shown very promising anti-cancer properties in vitro, but have yet to be evaluated in humans. Further study is required to determine the efficacy of these plant products in treating cancers in humans. This review will focus on the various plant-derived chemical compounds that have, in recent years, shown promise as anticancer agents and will outline their potential mechanism of action.

Cancer remains one of the leading causes of morbidity and mortality globally. Amongst the non-communicable diseases, cancer is the second leading cause of death, after cardiovascular disease . Cancer is responsible for one in eight deaths worldwide—more than AIDS, tuberculosis, and malaria together . Overall cancer incidence and mortality are higher in North America, Australia, New Zealand and Western Europe compared to the rest of the world . In the United States, one in four deaths is attributed to cancer. Globally, the number of cancer deaths is projected to increase from 7.1 million in 2002 to 11.5 million in 2030 .

Chemotherapy is routinely used for cancer treatment. Since cancer cells lose many of the regulatory functions present in normal cells, they continue to divide when normal cells do not. This feature makes cancer cells susceptible to chemotherapeutic drugs. Approximately five decades of systemic drug discovery and development have resulted in the establishment of a large collection of useful chemotherapeutic agents. However, chemotherapeutic treatments are not devoid of their own intrinsic problems. Various kinds of toxicities may occur as a result of chemotherapeutic treatments. For example, 5-fluorouracil, a common chemotherapeutic agent, is known to cause myelotoxicity, cardiotoxicity and has even been shown to act as a vasospastic agent in rare but documented cases . Another widely used chemodrug, doxorubicin causes cardiac toxicity , renal toxicity , and myelotoxicity . Similarly, bleomycin a well known chemotherapeutic agent, is known for its pulmonary toxicity . In addition, bleomycin shows cutaneous toxicity . Cyclophosphamide, a drug to treat many malignant conditions, has been shown to have bladder toxicity in the form of hemorrhagic cystitis, immunosuppression, alopecia and at high doses cardiotoxicity .

The toxicity of chemotherapeutic drugs sometimes creates a significant problem in the treatment of cancer using allopathy or established medicine. Various therapies have been propounded for the treatment of cancer, many of which use plant-derived products. There are four classes of plant-derived anticancer agents in the market today, the vinca alkaloids (vinblastine, vincristine and vindesine), the epipodophyllotoxins (etoposide and teniposide), the taxanes (paclitaxel and docetaxel) and the camptothecin derivatives (camptotecin and irinotecan). Plants still have enormous potential to provide newer drugs and as such are a reservoir of natural chemicals that may provide chemoprotective potential against cancer. Recently, Taneja and Qazi, have suggested a number of compounds from medicinal plants with potential anti-cancer activities .

RELATED : What Is GMO & How Do I Avoid It? ( Serious Health Risks Associated with GM Food Including infertility, Immune Problems)

This review will discuss some of the plant products that have recently been tested and may have potential in anticancer therapies. The possible mechanism of action of such plant products is also discussed.

Many studies have focused on the chemoprotective properties of plants such as anticarcinogenic properties of Abrus precatorius on Yoshida sarcoma in rats, fibrosarcoma in mice and ascites tumor cells . Similarly, Dhar et al. have examined the anticancer properties of Albizzia lebbeck on sarcoma in mice and Alstonia scholaries on benzo[a]pyrene-induced forestomach carcinoma in humans . Other plants that have shown anticarcinogenic properties include Anacardium occidentale in hepatoma, Asparagus racemosa in human epidermoid carcinoma, Boswellia serrata in human epidermal carcinoma of the nasopharynx, Erthyrina suberosa in sarcoma, Euphorbia hirta in Freund virus leukemia, Gynandropis pentaphylla in hepatoma, Nigella sativa in Lewis lung carcinoma, Peaderia foetida in human epidermoid carcinoma of the nasopharynx, Picrorrhiza kurroa in hepatic cancers, and Withania somnifera in various tumors .

The anticancer characteristics of a number of plants are still being actively researchedand some have shown promising results. Some plants and plant products that have shown promise as anticancer agents are discussed in detail in the following sections.

READ HERE ALL ARTICLE Anti-Cancer Herbs and Plants ( Efficacy of These Plant Products in Treating Cancers in Humans)