Myoepithelial cells are specialized cells that sit around the secretory units of your glands, combining properties of both muscle and skin-like (epithelial) tissue. They squeeze glandular structures to push out their products, whether that’s milk, saliva, sweat, or tears. Sometimes called “basket cells” because of their shape, they also serve as a structural barrier that plays a surprisingly important role in preventing cancer from spreading.
Where Myoepithelial Cells Are Found
These cells line the outside of secretory units in exocrine glands, which are glands that release their products through ducts. You’ll find myoepithelial cells in the mammary glands (breast tissue), the three major salivary glands (submandibular, sublingual, and parotid), the lacrimal glands (which produce tears), and both types of sweat glands in the skin. They also appear in the submucosal glands of the airways.
In each of these locations, myoepithelial cells occupy a specific position: they sit on top of the basement membrane (a thin structural sheet that separates tissues) but beneath the inner secretory cells that produce the gland’s actual product. This sandwiched position is key to how they function. They wrap around the secretory sacs (called acini or alveoli depending on the gland) and, in some glands, extend along the ducts as well.
What They Look Like
Under a microscope, myoepithelial cells are flat and star-shaped. Each cell has a central body with four to eight long arm-like extensions that branch out and wrap around the secretory unit, almost like fingers gripping a ball. This is why pathologists sometimes call them “stellate” (star-shaped) or “basket” cells. In cross-section, they can appear thin and spindle-shaped. Their internal structure reflects their dual nature: they contain contractile proteins similar to those in smooth muscle, while their outer surface has characteristics of epithelial (lining) tissue.
How They Contract
The defining feature of myoepithelial cells is their ability to contract and physically squeeze glandular secretions out through the ducts. They accomplish this using the same type of protein fibers found in smooth muscle cells, particularly a form of actin that generates contractile force. When this specific actin protein is missing, as demonstrated in mouse studies, the cells can still contract using backup proteins, but they generate significantly less force.
In the breast, this contraction is triggered by the hormone oxytocin. When a baby suckles, the brain releases oxytocin into the bloodstream. Within about seven minutes of oxytocin reaching the mammary gland, myoepithelial cells visibly tighten around the milk-producing sacs, collapsing them and forcing milk through the duct system toward the nipple. This is the “let-down reflex” that breastfeeding mothers experience. Blocking the oxytocin receptor on these cells prevents the contraction entirely.
The same basic mechanism operates in other glands. In salivary glands, myoepithelial contraction helps move saliva through the ductal system. In sweat glands, the secretory coil is formed by myoepithelial cells alongside the secretory cells, and their contraction aids in pushing sweat to the skin surface. In apocrine sweat glands (found in the armpits and groin), the myoepithelial cells have a unique feature: they directly interact with nerve endings, while the secretory cells do not.
Their Role as a Cancer Barrier
Beyond their contractile function, myoepithelial cells serve as a physical and biological barrier against cancer invasion, particularly in the breast. This is one of their most clinically significant roles.
In breast pathology, the intact myoepithelial layer is what distinguishes ductal carcinoma in situ (DCIS) from invasive ductal carcinoma. DCIS means cancer cells are still contained inside the ducts, surrounded by an intact layer of myoepithelial cells. Once tumor cells break through that myoepithelial layer and enter the surrounding tissue, the cancer is classified as invasive. This distinction fundamentally changes treatment decisions and prognosis.
To check whether the myoepithelial layer is intact, pathologists use stains that target proteins specific to these cells. The most commonly used markers are smooth muscle actin (SMA) and a protein called p63, both chosen for their reliable sensitivity and specificity. Calponin and smooth muscle myosin heavy chain are also used. Older markers like keratin 5 and S-100 protein have fallen out of favor because they sometimes stain the wrong cells, leading to unreliable results.
Myoepithelial cells also contribute to the basement membrane itself, producing structural proteins like laminin and type IV collagen. In normal breast tissue and benign breast conditions, these basement membrane proteins are present. In higher-grade invasive cancers, they disappear, reflecting the breakdown of the structural barriers that normally keep tissues organized.
Myoepithelial Cell Tumors
Myoepithelial cells themselves can give rise to tumors, most commonly in the salivary glands and head and neck region. A benign tumor made entirely of myoepithelial cells is called a myoepithelioma. These tumors lack destructive invasion, tissue death, abnormal cell shapes, and excessive cell division.
The malignant version, myoepithelial carcinoma, shares a similar cellular appearance but with critical differences: it shows destructively invasive growth into surrounding tissues, tends to invade nerves and blood vessels, has higher cellularity, more abnormal-looking cells, areas of tissue death, and increased cell division including abnormal forms. Destructive invasion into surrounding tissue is the hallmark feature that separates the malignant form from the benign one.
Role in Gland Development and Repair
During embryonic development, myoepithelial cells do more than just sit passively around forming glands. In the developing lacrimal and salivary glands, they surround the tips of the growing gland buds and release signaling molecules that encourage nearby cells to mature into functional secretory cells. They are active participants in shaping the gland’s architecture.
This developmental versatility persists in adults. In the airway submucosal glands, myoepithelial cells can proliferate, migrate, and transform into different cell types to help repair damaged airway surfaces after injury. This regenerative capacity makes them a type of reserve cell, able to step in when the tissue’s primary lining cells are lost.
Connection to Autoimmune Disease
Sjögren’s syndrome, an autoimmune condition that causes severe dry eyes and dry mouth, directly affects the glands where myoepithelial cells reside. The disease targets the lacrimal and salivary glands, causing inflammation and immune cell infiltration that disrupts normal gland function. Because myoepithelial contraction is essential for moving tears and saliva through their respective duct systems, damage to these cells contributes to the hallmark dryness that defines the condition.