Lymphatic spread of cancerous tumours. Light micrograph of a section through a large lymphatic vessel (white space) containing a clump of malignant (cancerous) neoplasms (dark pink, upper left), en route to a lymph node (not seen). A neoplasm is a mass of tissue that occurs due to an abnormal proliferation of cells (neoplasia). It is often called a tumour and can be either malignant or benign (non-cancerous). Movement through lymphatic vessels is a very common way that malignant tumours spread from epithelial layers.