Skip to 0 minutes and 15 seconds So what is a tumour? The word tumour literally means “a swelling.” But tumour is often used to mean the same as neoplasia. The word neoplasia literally means “new growth.” According to the pathologist Rupert Willis, writing a century ago, a tumour is “an abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of the normal tissues and persists in the same excessive manner after cessation of the stimuli which evoked the change.” Further definitions add that a tumour “is formed by an excessive, uncontrolled proliferation of cells as a result of an irreversible genetic change which is passed from one tumour cell to its progeny.” So a tumour is caused by genetic changes in DNA, which can be inherited.
Skip to 1 minute and 16 seconds This is different from normal body cells, which share the same DNA. What does a tumour look like? It is a collection of cells of the same tissue type usually lying together as a lump where a lump isn’t usual. Pathologist diagnose tumours mainly based on this abnormal appearance using the naked eye and using a microscope. The abnormal appearance involves both tissue architecture and individual cells. Normal tissues have clear structures and boundaries, which are shifted in tumours. Individual tumour cells look different from normal, with bigger, more variable nuclei, often with increased proliferation. This reflects the DNA changes in tumour cells. Once we have diagnosed the patient’s specimen as a tumour, how can we classify it?
Skip to 2 minutes and 11 seconds And thus how can we predict what will happen for the patient? The first way of classifying tumours is by their likely behaviour into benign and malignant. Malignant tumours are what is meant by the word “cancer.” The second way of classifying tumours is by tissue type. We will go through these in turn. So what are benign and malignant tumours? How do we tell them apart? And why is it important? In the patient, benign tumours do not invade. Instead their edge is smooth. Benign tumours stay where they started. In contrast, malignant tumours invade and destroy surrounding tissue. Invasion is one of the hallmarks of cancer and can be identified by the pathologist to help make the diagnosis.
Skip to 3 minutes and 5 seconds Once they have invaded, malignant tumours can spread to different sites where they can grow and form more tumour masses. Where the cancer started is called the “primary site” or “site of origin.” Cancer, which has spread somewhere else, is called there a secondary cancer or metastasis, meaning “change in place.” Cancer can spread via blood vessels or lymphatic channels. Looking down the microscope, malignant tumours usually look more abnormal and less like normal tissue than do benign tumours. If benign tumours cause problems for the patient, it is usually because the tumour is pressing on an important adjacent structure or making more hormones than usual. Malignant tumours cause problems by forming lumps and destroying normal tissue at both primary and metastatic sites.
Skip to 4 minutes and 3 seconds So malignant tumours often lead to the death of patients while benign tumours very rarely do. Now we’ll look at how to classify tumours using the broad categories of tissue we talked about earlier. Each broad category has malignant tumours. Some also include benign tumours. Further classification uses tissue subtype and sometimes organ site. Let’s go through the broad categories in turn, epithelium first. Benign epithelial tumours are called papillomas or adenomas. Malignant epithelial tumours are carcinomas. These can be divided into squamous carcinomas, adenocarcinomas, which develop from glandular epithelium lining tubes and carcinomas of specific organs, like hepatocellular carcinoma from the liver. Carcinomas are the most common broad tumour type overall. Common examples include lung squamous carcinoma and breast, prostate, colorectal, or prostatic adenocarcinoma.
Skip to 5 minutes and 15 seconds Let’s go through the other broad categories. Malignant connective tissue tumours are called sarcomas. Leukaemia and lymphoma are malignant tumours of the blood and lymphoid system. Nervous system tumours include gliomas. Other tumour types include malignant melanoma, germ cell tumours, malignant mesothelioma, and childhood blastomas. Lastly, let’s talk about dysplasia. Dysplasia is a benign tumour of epithelial cells or melanocytes. It can be a stage between cell injury and cancer. Dysplasia is sometimes called “intraepithelial” or “in situ” neoplasia. Down the microscope, dysplasia can be seen as abnormal neoplastic cells, which are still in the epithelium and haven’t invaded beyond. Dysplasia is an important stage in the development of many carcinomas.
Skip to 6 minutes and 12 seconds Here is a famous diagram showing how dysplasia might fit in multi-step progression from normal epithelium to invasive carcinoma and beyond. Dysplasia often doesn’t cause symptoms but detection of dysplasia is the aim of some of the cancer screening programmes like the cervical cancer screening programme. If, detected then dysplasia can be removed and, potentially, progression to invasive carcinoma prevented. In this video, we’ve learned about how cancers develop, look, and behave. We’ve talked about how we name or classify tumours into benign and malignant and by tissue type and site. In the next cancer pathology lecture, we’ll talk more about cancer spread and symptoms. We’ll describe how we look at tumours in real patient samples, including tumour grading and staging.
Skip to 7 minutes and 12 seconds We’ll also talk about additional tests currently used for specific molecular abnormalities. We know that tumour classification or diagnosis helps to predict how cancers will behave and how best to treat patients. In the next week, we’ll learn how these classifications may be transformed through genomics.
Cancer pathology: what's in a name? Part two
Dr Karin Oien introduces the role of pathology in cancer. This is part two of a two-part video.
At the end of this video Dr Oien describes some material that is ‘Coming Soon’ - you’ll see this during week four of the course.
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