In pathology, the term malignant transformation describes the development of a malignant (cancerous) tumour from a benign (noncancerous) tumour or a precancerous disease. Malignant transformation is important because the cells in the malignant tumour can grow into nearby tissues and metastasize (spread) to distant organs such as lymph nodes and the lungs.
Common conditions that can undergo malignant transformation
Examples of benign (noncancerous) or precancerous conditions that can undergo malignant transformation include:
- Colonic polyps: These are growths found on the inner lining of the colon. While many are benign, some types, especially adenomatous polyps (adenomas), can transform into colorectal cancer if not removed.
- Actinic keratosis: This is a rough, scaly patch on the skin caused by years of sun exposure. It is considered a precancerous condition that can transform into squamous cell carcinoma of the skin.
- Barrett’s esophagus: This condition is caused by chronic acid reflux, where the lining of the esophagus changes to resemble the lining of the intestine. This can lead to esophageal adenocarcinoma.
- Cervical dysplasia: This term refers to abnormal changes in the cells on the surface of the cervix, often detected through a Pap smear. High grade dysplasia is considered precancerous and can develop into cervical cancer.
- Leukoplakia: This is a white patch that can appear on the tongue, the inside of the cheek, or other areas of the mouth. It is often associated with smoking or other irritants. Leukoplakia can transform into oral squamous cell carcinoma.
- Dysplastic nevus (atypical mole): These are unusual-looking moles that can be larger than normal moles and have irregular borders and colors. They have a higher risk of transforming into melanoma, a dangerous type of skin cancer.
- Atypical endometrial hyperplasia: This condition involves the thickening of the uterus lining and is often caused by excess estrogen without progesterone. If left untreated it can progress to endometrial cancer.
Microscopic features of malignant transformation
- Cells that vary widely in size and shape: In healthy tissue, cells look quite uniform. If cells start to look very different from each other, it can be a sign of cancer. Pathologists describe these cells as pleomorphic.
- Increased number of dividing cells: Cancer cells often grow and divide more rapidly than normal cells. Pathologists can see signs of this rapid division under the microscope. Cells divide by a process called mitosis and a dividing cell is called a mitotic figure.
- Abnormal nuclei: The nucleus is like the control center of the cell, containing its DNA. In cancer cells, the nuclei might be larger or oddly shaped, indicating abnormal activity. A nucleus that is darker than normal is called hyperchromatic.
- Loss of normal tissue structure: Healthy tissues have an organized structure. Cancer can disrupt this organization, with cells invading into areas where they don’t belong.
- Ability to invade nearby tissues or form new blood vessels: Cancer cells can break away from where they started and invade into surrounding tissues. They might also start forming their blood vessels to feed themselves, a process called angiogenesis.