76 SCIENCE AND CULTURE, MARCH-APRIL, 2014 CANCER STEM CELLS AND MULTIPLE DRUG RESISTANCE IN BREAST CANCER* A. MUKHOPADHYAY**, A. CHAKRABORTY, S. MUKHOPADHYAY AND J BASAK Million of new cancer patients are diagnosed each year and over half of these patients die from this disease. As the second leading cause of cancer deaths, breast cancer in estimated to be diagnosed in over one million people worldwide and to cause more than 400,000 deaths each year. Chemotherapy is part of a successful treatment to many cases; however, the development of multidrug resistance (MDR) to it becomes a major obstacle so as to as few as half of the breat cancer patients treated benefit from chemotherapy. MDR is a term used to describe the phenomenon characterized by the ability of drug resistant tumors to exhibit simultaneous resistnace to a number of structurally and functionally unrelated chemotherapeutic agents. At present, many mechanisms have been found to be responsible for it, including over expression of the members of the adenosine triphosphate (ATP)-binding cassette (ABC) membrane transporter family, changes of apoptosis- related genes, the alteration of DNA repair gene, cancer stem cells and so on. And up to date, many methods were adopted to overcome MDR, for example natural drugs, chemical drugs and genetic therapy. Advanced cases of breast cancer with 2nd line of treatment failure are chemo- resistant and high in BCSCs. Herein, we will use an aggressive approach to test for best chemo- and/or targeted therapy on BCSCs. ARTICLE * Second Ila Roy Memorial Lecture Organised by ISNA delivered on 30th September, 2013. ** Netaji Subhas Chandra Bose Cancer Research Institute, Kolkata e-mail : hmcwt@dataone.in Introduction B reast cancer is the most common form of cancer diagnosed in women worldwide. Although the rate of mortality as a result of breast cancer has decreased in western countries due to early detection, it is now the leading cause of cancer death (about 60%) among females in economically developing countries. Thirty percent of the breast cancers in India are in the second or third decade of life and they are resistant to conventional mode of therapies. The concept of cancer stem cells responsible for tumor origin, maintenance, and resistance to treatment has gained prominence in the field of breast cancer research. The therapeutic targeting of these cells has the potential to eliminate residual disease and may become an important component of a multimodality treatment. In the past two decades, more than thirty new anticancer drugs have been introduced, but survival rates have improved only marginally for many forms of cancer. In contrast to most cancer cells, cancer stem cells are slow- dividing and have a lowered ability to undergo apoptosis and a higher ability of DNA repair, making them more resistant to traditional methods of cancer treatment. Breast cancer, the most common form of cancer amongst women, also has the second highest morbidity rate in the world (10.9% of all cancers). With an estimated 1.38 million new cancer cases diagnosed in 2008, it is also the most common cancer both in developed and developing regions (Globocan cancer fact sheet, 2008). In spite of much advancement in breast cancer treatments over the years, relapse of this disease with time (approximately 40% of all breast cancer patients with 60-70% relapse cases with metastasis) serves as a major roadblock in complete cure;