**2. Stromal cells and cancer metastasis**

Normally, cells in the human body undergo continuous cellular division to ensure proliferation and differentiation of cells, and removal of damaged/worn-out cells (apoptosis) to ensure balance in the cellular system. Cancer arises when there's uncontrolled growth and/or proliferation of cells in the body without apoptosis. Cancer can emanate anywhere in the human body, and these cancer cells can be benign or malignant. In addition, cancer cells can metastasize or spread into, or invade nearby tissues and can travel to distant places in the body to form new tumours [19, 20].

Cancer cells spread either by invasion of nearby tissues or by movement through the lymphatic and blood vessels. Although different cancers are more likely to spread to downstream organs and lymph nodes close to its primary sites than others, most common metastatic areas include the liver, lung, and bone [19, 20]. Most of the cancers that separate from the original tumour do not survive as they also require the capacity to adhere to the blood or lymph vessels, grow and thrive in the new site as well as evade the attacks from the immune system [20].

However, it is noteworthy to mention that not all cancer cells are metastatic and not all cells within the metastatic tumour have the potential to metastasize [21]. The essential hallmarks of metastasis can be difficult to ascribe since they are superimposed by that of cancer itself, however, these five qualities have been reported

and includes: dissemination (detachment) and invasion, intravasation, circulation, extravasation, and colonisation [12, 22].
