Neoplasia is new, uncontrolled growth of cells that is not under physiologic control. A "tumor" or "mass lesion" is simply a "growth" or "enlargement" which may not be neoplastic (such as a granuloma). The term "cancer" implies malignancy, but neoplasms can be subclassified as either benign or malignant.
There is no single mechanism by which a neoplasm arises. Many different mechanisms give rise to neoplasms, and that is what makes diagnosis and treatment so challenging.
The word "cancer" or "malignancy" strikes fear in a patient hearing it for the first time. It is likely nothing else will be heard or remembered soon after that. Provide empathy, "I know that this can be very difficult to hear." At a follow-up session, more details regarding a treatment plan can be discussed. Some urgency is required, as the survival for the average cancer, such as a breast cancer, decreases by 1% per month of delayed diagnosis and treatment.