PIK3CA Gene

An epidermal nevus (plural: nevi) is an abnormal, noncancerous (benign) patch of skin caused by an overgrowth of cells in the outermost layer of skin (epidermis). Epidermal nevi are typically seen at birth or develop in early childhood. Affected individuals have one or more nevi that vary in size.

There are several types of epidermal nevus that are defined in part by the type of epidermal cell involved. The epidermis is composed primarily of a specific cell type called a keratinocyte. One group of epidermal nevi, called keratinocytic or nonorganoid epidermal nevi, includes nevi that involve only keratinocytes. Keratinocytic epidermal nevi are typically found on the torso or limbs. They can be flat, tan or brown patches of skin or raised, velvety patches. As affected individuals age, the nevi can become thicker and darker and develop a wart-like (verrucous) appearance. Often, keratinocytic epidermal nevi follow a pattern on the skin known as the lines of Blaschko. The lines of Blaschko, which are normally invisible on skin, are thought to follow the paths along which cells migrate as the skin develops before birth. Keratinocytic epidermal nevi are also known as linear epidermal nevi or verrucous epidermal nevi, based on characteristics of their appearance.

Other types of epidermal nevi involve additional types of epidermal cells, such as the cells that make up the hair follicles, the sweat glands, or the sebaceous glands (glands in the skin that produce a substance that protects the skin and hair). These nevi comprise a group called organoid epidermal nevi. A common type of organoid epidermal nevus is called nevus sebaceous. Nevi in this group are waxy, yellow-orange patches of skin, usually on the scalp or face. The patch is typically hairless, leaving a distinct region of baldness (alopecia). Similar to keratinocytic epidermal nevi, nevi sebaceous can become thicker and more verrucous over time. In about one-quarter of people with a nevus sebaceous, a tumor forms in the same region as the nevus. The tumor is usually benign, although rarely cancerous (malignant) tumors develop.

Some affected individuals have only an epidermal nevus and no other abnormalities. However, sometimes people with an epidermal nevus also have problems in other body systems, such as the brain, eyes, or bones. In these cases, the affected individual has a condition called an epidermal nevus syndrome. There are several different epidermal nevus syndromes characterized by the type of epidermal nevus involved.

Cowden syndrome is a genetic disorder characterized by multiple noncancerous, tumor-like growths called hamartomas and an increased risk of developing certain cancers.

Almost everyone with Cowden syndrome develops hamartomas. These growths are most commonly found on the skin and mucous membranes (such as the lining of the mouth and nose), but they can also occur in the intestine and other parts of the body. The growth of hamartomas on the skin and mucous membranes typically becomes apparent by a person's late twenties.

Cowden syndrome is associated with an increased risk of developing several types of cancer, particularly cancers of the breast, a gland in the lower neck called the thyroid, and the lining of the uterus (the endometrium). Other cancers that have been identified in people with Cowden syndrome include kidney cancer, colorectal cancer, and an agressive form of skin cancer called melanoma. Compared with the general population, people with Cowden syndrome develop these cancers at younger ages, often beginning in their thirties or forties. People with Cowden syndrome are also more likely to develop more than one cancer during their lifetimes compared to the general population. Other diseases of the breast, thyroid, and endometrium are also common in Cowden syndrome. Additional signs and symptoms can include an enlarged head (macrocephaly) and a rare, noncancerous brain tumor called Lhermitte-Duclos disease. A small percentage of affected individuals have delayed development, intellectual disability, or autism spectrum disorder, which can affect communication and social interaction.

Some people do not meet the strict criteria for a clinical diagnosis of Cowden syndrome, but they have some of the characteristic features of the condition, particularly the cancers. These individuals are often described as having Cowden-like syndrome. Both Cowden syndrome and Cowden-like syndrome are caused by mutations in the same genes.

The features of Cowden syndrome overlap with those of another disorder called Bannayan-Riley-Ruvalcaba syndrome. People with Bannayan-Riley-Ruvalcaba syndrome also develop hamartomas and other noncancerous tumors.  Some people with Cowden syndrome have relatives diagnosed with Bannayan-Riley-Ruvalcaba syndrome, and other affected individuals have the characteristic features of both conditions. Based on these similarities, researchers have proposed that Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome represent a spectrum of overlapping features known as PTEN hamartoma tumor syndrome (named for the genetic cause of the conditions) instead of two distinct conditions.

Megalencephaly-capillary malformation syndrome (MCAP) is a disorder characterized by overgrowth of several tissues in the body. Its primary features are a large brain (megalencephaly) and abnormalities of small blood vessels in the skin called capillaries (capillary malformations).

In individuals with MCAP, megalencephaly leads to an unusually large head size (macrocephaly), which is typically evident at birth. After birth, the brain and head continue to grow at a fast rate for the first few years of life; then, the growth slows to a normal rate, although the head remains larger than average. Additional brain abnormalities are common in people with MCAP; these can include excess fluid within the brain (hydrocephalus) and abnormalities in the brain's structure, such as those known as Chiari malformation and polymicrogyria. Abnormal brain development leads to intellectual disability in most affected individuals and can also cause seizures or weak muscle tone (hypotonia). In particular, polymicrogyria is associated with speech delays and difficulty chewing and swallowing.

The capillary malformations characteristic of MCAP are composed of enlarged capillaries that increase blood flow near the surface of the skin. These malformations usually look like pink or red spots on the skin. In most affected individuals, capillary malformations occur on the face, particularly the nose, the upper lip, and the area between the nose and upper lip (the philtrum). In other people with MCAP, the malformations appear as patches spread over the body or as a reddish net-like pattern on the skin (cutis marmorata).

In some people with MCAP, excessive growth affects not only the brain but other individual parts of the body, which is known as segmental overgrowth. This can lead to one arm or leg that is bigger or longer than the other or a few oversized fingers or toes. Some affected individuals have fusion of the skin between two or more fingers or toes (cutaneous syndactyly).

Additional features of MCAP can include flexible joints and skin that stretches easily. Some affected individuals are said to have doughy skin because the tissue under the skin is unusually thick and soft.

The gene involved in MCAP is also associated with several types of cancer. Only a small number of individuals with MCAP have developed tumors (in particular, a childhood form of kidney cancer known as Wilms tumor and noncancerous tumors in the nervous system known as meningiomas).

Breast cancer is a disease in which certain cells in the breast become abnormal and multiply uncontrollably to form a tumor. Although breast cancer is much more common in women, this form of cancer can also develop in men. In both women and men, the most common form of breast cancer begins in cells lining the milk ducts (ductal cancer). In women, cancer can also develop in the glands that produce milk (lobular cancer). Most men have little or no lobular tissue, so lobular cancer in men is very rare.

In its early stages, breast cancer usually does not cause pain and may exhibit no noticeable symptoms. As the cancer progresses, signs and symptoms can include a lump or thickening in or near the breast; a change in the size or shape of the breast; nipple discharge, tenderness, or retraction (turning inward); and skin irritation, dimpling, redness, or scaliness. However, these changes can occur as part of many different conditions. Having one or more of these symptoms does not mean that a person definitely has breast cancer.

In some cases, cancerous cells can invade surrounding breast tissue. In these cases, the condition is known as invasive breast cancer. Sometimes, tumors spread to other parts of the body. If breast cancer spreads, cancerous cells most often appear in the bones, liver, lungs, or brain. Tumors that begin at one site and then spread to other areas of the body are called metastatic cancers.

A small percentage of all breast cancers cluster in families. These cancers are described as hereditary and are associated with inherited gene mutations. Hereditary breast cancers tend to develop earlier in life than noninherited (sporadic) cases, and new (primary) tumors are more likely to develop in both breasts.