EIN lesions have been discovered by a combination of molecular, histologic, and clinical outcome studies beginning in the 1990s which provide a multifaceted characterization of this disease. They are a subset of a larger mixed group of lesions previously called "endometrial hyperplasia". The EIN diagnostic schema is intended to replace the previous "endometrial hyperplasia" classification as defined by the World Health Organization in 1994, which have been separated into benign (benign endometrial hyperplasia) and premalignant (EIN) classes in accordance with their behavior and clinical management.

EIN should not be confused with an unrelated entity, serous intraepithelial carcinoma ("serous EIC"), which is an early stage of a different tumor type known as papillary serous adenocarcinoma that also occurs in the same location within the uterus.

Endometrial intraepithelial neoplasia (EIN) is a premalignant lesion of the uterine lining that predisposes to endometrioid endometrial adenocarcinoma. It is composed of a collection of abnormal endometrial cells, arising from the glands that line the uterus, which have a tendency over time to progress to the most common form of uterine cancer—endometrial adenocarcinoma, endometrioid type.

Endometrial hyperplasia is a condition of excessive proliferation of the cells of the endometrium, or inner lining of the uterus.

Most cases of endometrial hyperplasia result from high levels of estrogens, combined with insufficient levels of the progesterone-like hormones which ordinarily counteract estrogen's proliferative effects on this tissue. This may occur in a number of settings, including obesity, polycystic ovary syndrome, estrogen producing tumours (e.g. granulosa cell tumour) and certain formulations of estrogen replacement therapy. Endometrial hyperplasia is a significant risk factor for the development or even co-existence of endometrial cancer, so careful monitoring and treatment of women with this disorder is essential.

Uterine serous carcinoma (USC), also known as uterine papillary serous carcinoma (UPSC) and uterine serous adenocarcinoma, is an uncommon form of endometrial cancer that typically arises in postmenopausal women.

It is typically diagnosed on endometrial biopsy, prompted by post-menopausal bleeding.

Unlike the more common low-grade "endometrioid endometrial adenocarcinoma", USC does not develop from endometrial hyperplasia and is not hormone-sensitive. It arises in the setting of endometrial atrophy and is classified as a type II endometrial cancer.

The lesion is found in patients who present typically with abnormal or postmenopausal bleeding. Such bleeding is followed by further evaluation leading to a tissue diagnosis, usually done by a dilatation and curettage (D&C). A work-up to follow would look for metastasis using imaging technology including sonography and MRI. The median age at diagnosis in a study of 138 women was 67 years, of these 54 had stage I, 20 stage II, 41 stage III, and 23 stage IV disease.

Histopathologically, uterine serous carcinomas is typically characterized by (1) nipple-shaped structures (papillae) with fibrovascular cores (2) marked nuclear atypia (irregularies in the nuclear membrane, enlarged nuclear size), (3) psammoma bodies and (4) cilia.

Vaginal bleeding or spotting in women after menopause occurs in 90% of endometrial cancer. Bleeding is especially common with adenocarcinoma, occurring in two-thirds of all cases. Abnormal menstrual cycles or extremely long, heavy, or frequent episodes of bleeding in women before menopause may also be a sign of endometrial cancer.

Symptoms other than bleeding are not common. Other symptoms include thin white or clear vaginal discharge in postmenopausal women. More advanced disease shows more obvious symptoms or signs that can be detected on a physical examination. The uterus may become enlarged or the cancer may spread, causing lower abdominal pain or pelvic cramping. Painful sexual intercourse or painful or difficult urination are less common signs of endometrial cancer. The uterus may also fill with pus (pyometrea). Of women with these less common symptoms (vaginal discharge, pelvic pain, and pus), 10–15% have cancer.

Like other hyperplastic disorders, endometrial hyperplasia initially represents a physiological response of endometrial tissue to the growth-promoting actions of estrogen. However, the gland-forming cells of a hyperplastic endometrium may also undergo changes over time which predispose them to cancerous transformation. Several histopathology subtypes of endometrial hyperplasia are recognisable to the pathologist, with different therapeutic and prognostic implications. The most commonly used classification system for endometrial hyperplasia is the World Health Organization system, which has four categories: simple hyperplasia without atypia, complex hyperplasia without atypia, simple atypical hyperplasia and complex atypical hyperplasia.

- Endometrial hyperplasia (simple or complex) - Irregularity and cystic expansion of glands (simple) or crowding and budding of glands (complex) without worrisome changes in the appearance of individual gland cells. In one study, 1.6% of patients diagnosed with these abnormalities eventually developed endometrial cancer.

- Atypical endometrial hyperplasia (simple or complex) - Simple or complex architectural changes, with worrisome ("atypical") changes in gland cells, including cell stratification, tufting, loss of nuclear polarity, enlarged nuclei, and an increase in mitotic activity. These changes are similar to those seen in true cancer cells, but atypical hyperplasia does not show invasion into the connective tissues, the defining characteristic of cancer. The previously mentioned study found that 22% of patients with atypical hyperplasia eventually developed cancer.

Atypical ductal hyperplasia, abbreviated ADH, is the term used for a benign lesion of the breast that indicates an increased risk of breast cancer.

The name of the entity is descriptive of the lesion; ADH is characterized by cellular proliferation (hyperplasia) within one or two breast ducts and (histomorphologic) architectural abnormalities, i.e. the cells are arranged in an abnormal or atypical way.

In the context of a core (needle) biopsy, ADH is considered an indication for a breast lumpectomy, also known as a surgical (excisional) biopsy, to exclude the presence of breast cancer.

The lesion is found in patients who present typically with abnormal or postmenopausal bleeding or discharge. Such bleeding is followed by further evaluation leading to a tissue diagnosis, usually done by a dilatation and curettage (D&C). A work-up to follow would look for metastasis using imaging technology including sonography and MRI. The median age at diagnosis in a large study was 66 years. Histologically the lesion may coexist with classical endometrial cancer.

Endometrial stromal tumors are a group of stromal tumors of the uterus of low to high-grade of malignity.

Endometrial stromal sarcoma is a malignant subtype of endometrial stromal tumor arising from the stroma (connective tissue) of the endometrium rather than the glands. There are three grades for endometrial stromal tumors, as follows. It was previously known as "endolymphatic stromal myosis" because of diffuse infiltration of myometrial tissue or the invasion of lymphatic channels.

APAs are characterized by glands with abnormal shapes that: (1) often have squamous metaplasia, and (2) are surrounded by benign smooth muscle. Nuclear atypia, if present, is mild.

The microscopic differential diagnosis includes endometrial carcinoma and endocervical adenocarcinoma.

The uterine sarcomas form a group of malignant tumors that arises from the smooth muscle or connective tissue of the uterus.

An endometrial polyp or uterine polyp is a mass in the inner lining of the uterus. They may have a large flat base (sessile) or be attached to the uterus by an elongated (pedunculated). Pedunculated polyps are more common than sessile ones. They range in size from a few millimeters to several centimeters. If pedunculated, they can protrude through the cervix into the vagina. Small blood vessels may be present, particularly in large polyps.

They often cause no symptoms. Where they occur, symptoms include irregular menstrual bleeding, bleeding between menstrual periods, excessively heavy menstrual bleeding (menorrhagia), and vaginal bleeding after menopause. Bleeding from the blood vessels of the polyp contributes to an increase of blood loss during menstruation and blood "spotting" between menstrual periods, or after menopause. If the polyp protrudes through the cervix into the vagina, pain (dysmenorrhea) may result.

The terms uterine cancer and womb cancer may refer to any of several different types of cancer which occur in the uterus, namely:

- Endometrial cancer:

- Cervical cancer arises from the transformation zone of the cervix, the lower portion of the uterus and connects to the upper aspect of the vagina.

- Uterine sarcomas: sarcomas of the myometrium, or muscular layer of the uterus, are most commonly leiomyosarcomas.

- Gestational trophoblastic disease relates to neoplastic processes originating from tissue of a pregnancy that often is located in the uterus.

ADH, generally, is asymptomatic. It usually comes to medical attention on a screening mammogram, as a non-specific suspicious abnormality that requires a biopsy.

Uterine cancer, also known as womb cancer, is any type of cancer that emerges from the tissue of the uterus. It can refer to several types of cancer, with cervical cancer (arising from the lower portion of the uterus) being the most common type worldwide and the second most common cancer in women in developing countries. Endometrial cancer (or cancer of the inner lining of the uterus) is the second most common type, and fourth most common cancer in women from developed countries.

Risk factors depend on specific type, but obesity, older age, and human papillomavirus infection add the greatest risk of developing uterine cancer. Early on, there may be no symptoms, but irregular vaginal bleeding, pelvic pain or fullness may develop. If caught early, most types of uterine cancer can be cured using surgical or medical methods. When the cancer has extended beyond the uterine tissue, more advanced treatments including combinations of chemotherapy, radiation therapy, or surgery may be required.

Endometrial cancer is a cancer that arises from the endometrium (the lining of the uterus or womb). It is the result of the abnormal growth of cells that have the ability to invade or spread to other parts of the body. The first sign is most often vaginal bleeding not associated with a menstrual period. Other symptoms include pain with urination, pain during sexual intercourse, or pelvic pain. Endometrial cancer occurs most commonly after menopause.

Approximately 40% of cases are related to obesity. Endometrial cancer is also associated with excessive estrogen exposure, high blood pressure and diabetes. Whereas taking estrogen alone increases the risk of endometrial cancer, taking both estrogen and a progestogen in combination, as in most birth control pills, decreases the risk. Between two and five percent of cases are related to genes inherited from the parents. Endometrial cancer is sometimes loosely referred to as "uterine cancer", although it is distinct from other forms of uterine cancer such as cervical cancer, uterine sarcoma, and trophoblastic disease. The most frequent type of endometrial cancer is endometrioid carcinoma, which accounts for more than 80% of cases. Endometrial cancer is commonly diagnosed by endometrial biopsy or by taking samples during a procedure known as dilation and curettage. A pap smear is not typically sufficient to show endometrial cancer. Regular screening in those at normal risk is not called for.

The leading treatment option for endometrial cancer is abdominal hysterectomy (the total removal by surgery of the uterus), together with removal of the fallopian tubes and ovaries on both sides, called a bilateral salpingo-oophorectomy. In more advanced cases, radiation therapy, chemotherapy or hormone therapy may also be recommended. If the disease is diagnosed at an early stage, the outcome is favorable, and the overall five-year survival rate in the United States is greater than 80%.

In 2012, endometrial cancers newly occurred in 320,000 women and caused 76,000 deaths. This makes it the third most common cause of death in cancers which only affect women, behind ovarian and cervical cancer. It is more common in the developed world and is the most common cancer of the female reproductive tract in developed countries. Rates of endometrial cancer have risen in a number of countries between the 1980s and 2010. This is believed to be due to the increasing number of elderly people and increasing rates of obesity.

Radial scars are diagnosed by a microscopic examination of excised tissue, i.e. they are diagnosed by pathologists based on their histomorphology.

A malignant mixed Müllerian tumor, also known as malignant mixed mesodermal tumor, MMMT and carcinosarcoma, is a malignant neoplasm found in the uterus, the ovaries, the fallopian tubes and other parts of the body that contains both carcinomatous (epithelial tissue) and sarcomatous (connective tissue) components. It is divided into two types, homologous (in which the sarcomatous component is made of tissues found in the uterus such as endometrial, fibrous and/or smooth muscle tissues) and a heterologous type (made up of tissues not found in the uterus, such as cartilage, skeletal muscle and/or bone). MMMT account for between two and five percent of all tumors derived from the body of the uterus, and are found predominantly in postmenopausal women with an average age of 66 years. Risk factors are similar to those of adenocarcinomas and include obesity, exogenous estrogen therapies, and nulliparity. Less well-understood but potential risk factors include tamoxifen therapy and pelvic irradiation.

Low-grade endometrial stromal sarcoma consists of cells resembling normal proliferative phase endometrium, but with infiltration or vascular invasion. These behave less aggressively, sometimes metastasizing, with cancer stage the best predictor of survival. The cells express estrogen/progesterone-receptors.

Uterine clear-cell carcinoma (CC) is a rare form of endometrial cancer with distinct morphological features on pathology; it is aggressive and has high recurrence rate. Like uterine papillary serous carcinoma CC does not develop from endometrial hyperplasia and is not hormone sensitive, rather it arises from an atrophic endometrium. Such lesions belong to the type II endometrial cancers.

In breast pathology, a radial scar of the breast, formally radial scar of the breast, is a benign breast lesion that can radiologically mimic malignancy, i.e. cancer.

Radial scar is associated with atypia and/or malignancy and may be an independent risk factor for the development of carcinoma in either breast.

Atypical polypoid adenomyoma, abbreviated APA, is a rare uncommon benign tumour of the uterus.