Stroma is the connective tissue just below the surface of an organ. It is a special type of tissue that helps hold the other parts of the organ together. Stroma is made up of cells that give the tissue its strength and shape. Many of these cells are called fibroblasts and pathologists often describe them as spindle cells because they are long and thin. Stroma also includes blood vessels that bring nutrients to the tissue and lymphatic channels that remove excess fluid and waste.
The way stroma looks when viewed under the microscope changes in response to injury or cancer. Desmoplasia is a word pathologists use to describe the look of the tissue after it has come in contact with cancer cells. The movement of cancer cells into a tissue is called invasion and pathologists look for desmoplasia when trying to decide if a tumour is benign or malignant. Reactive stroma is a term pathologists use to describe non-cancerous changes. Even though the changes in the reactive stroma are non-cancerous, they can be seen in the tissue surrounding a tumour. Reactive stroma is also commonly seen in tissue that has been damaged by trauma, inflammation, or a prior medical treatment such as surgery or radiation.