Hamartomas, while generally benign, can cause problems due to their location. For example, when located on the skin, especially on the face or neck, they can be very disfiguring. Cases have been reported of hamartomas the size of a small orange. They may obstruct practically any organ in the body, such as the colon, eye, etc. They are particularly likely to cause major health issues when located in the hypothalamus, kidneys, lips, or spleen. They can be removed surgically if necessary, and are not likely to recur. Prognosis will depend upon the location and size of the lesion, as well as the overall health of the patient.

Large and especially giant congenital nevi are at higher risk for malignancy degeneration into melanoma. Because of the premalignant potential, it is an acceptable clinical practice to remove congenital nevi electively in all patients and relieve the nevocytic overload.

Papillary eccrine adenoma (also known as "tubular apocrine adenoma") is a cutaneous condition characterized by an uncommon benign sweat gland neoplasm that presents as a dermal nodule located primarily on the extremities of black patients.

Folliculosebaceous cystic hamartoma abbreviated as (FSCH) is a rare cutaneous hamartoma consisting of dilated folliculosebaceous units invested in mesenchymal elements. it typically affects adults, have a predilection for the central face or scalp, with less than 1.5 cm dimension. Clinically, the lesions are asymptomatic, rubbery to firm in consistency, and usually occur on or above the neck in (> 90%) of cases, Histopathologically, FSCH shares several similar features to sebaceous trichofolliculoma, but it is usually possible to differentiate these two tumors.

Hamartomas result from an abnormal formation of normal tissue, although the underlying reasons for the abnormality are not fully understood. They grow along with, and at the same rate as, the organ from whose tissue they are made, and, unlike cancerous tumors, only rarely invade or compress surrounding structures significantly.

Most juvenile polyps are benign, however, malignancy can occur. The cumulative lifetime risk of colorectal cancer is 39% in patients with juvenile polyposis syndrome.

A folliculosebaceous-apocrine hamartoma, also known as "follicular-apocrine hamartoma", is a benign proliferation of the folliculosebaceous-apocrine unit.

Spiradenoma, also spiroma or eccrine spiradenoma, is a cutaneous condition that is typically characterized, clinically, as a solitary, deep-seated dermal nodule of approximately one centimeter, occurring on the ventral surface of the body. Spiradenoma lesions are benign sudoriferous tumors, and have also been described as cystic epitheliomas of the sweat glands.

The histological origin is controversial.

There are a number of acquired causes of local gigantism. A body part can attain bigger size from causes as common as the following:

- inflammation, due to trauma or infection

- tumors like osteoid osteoma, melorheostosis, and lipofibromatous hamartoma

- Arteriovenous malformations occurring on a limb, before the closure of epiphyses in long bones

- Elephantiasis, which is quite common in south-east asia due to prevalence of filariasis.

- Still's disease

- amyloidosis

- acromegaly

Mucinous nevus (also known as "Nevus mucinosus") is a rare cutaneous condition characterized by hamartoma that can be congenital or acquired.

Choristomas, forms of heterotopia, are closely related benign tumors, found in abnormal locations.

It is different from hamartoma. The two can be differentiated as follows: a hamartoma is disorganized overgrowth of tissues in their normal location, (eg, Peutz-Jeghers polyps) while a choristoma is normal tissue growth in an abnormal location (e.g., gastric tissue located in distal ileum in Meckel diverticulum).

Fibrous hamartoma of infancy is a rapidly growing, painless, ill-defined subcutaneous or intradermal nodule that is generally solitary and less than 5 cm in size, though, rarely, multiple lesions occur synchronously.

By 1999, there were 12 reported cases.

The majority of patients are less than 2 years old, with 25% of cases being congenital. Possible locations include the trunk and limbs; usually the upper arm or shoulder. Local excision is the treatment of choice, but it may recur locally.

Congenital causes include:

- Klippel Trenaunay Weber syndrome

- Maffucci syndrome

- macrodystrophia lipomatosa

- neurofibromatosis,

- lipoatrophic diabetes.

- Proteus syndrome, which by one theory accounts for the deformities of the Elephant Man

A basaloid follicular hamartoma is a cutaneous condition characterized as distinctive benign adnexal tumor that has several described variants.

Because Cowden syndrome can be difficult to diagnose, the exact prevalence is unknown; however, it probably occurs in at least 1 in 200,000 people.

A 2010 review of 211 patients (21 from one center, and the remaining 190 from the external literature) studied the risks for cancer and Lhermitte-Duclos disease in Cowden syndrome patients.

The cumulative lifetime (age 70 years) risks were 89% for any cancer diagnosis (95% confidence interval (CI) = 80%,95%), breast cancer [female] 81% (CI = 66%,90%), LDD 32% (CI = 19%,49%), thyroid cancer 21% (CI = 14%,29%), endometrial cancer 19% (CI = 10%,32%) and renal cancer 15% (CI = 6%,32%). A previously unreported increased lifetime risk for colorectal cancer was identified (16%, CI = 8%,24%). Male CS patients had fewer cancers diagnosed than female patients and often had cancers not classically associated with CS.

A 2006 review stated that RS often leads renal cancer between ages 30-50. Renal cancer kills about 1 in 3 people, but 5-year survival rates improved between 1974-1976 and 1995-2000, from 52% to 64%.

Lhermitte–Duclos disease is a rare entity; approximately 222 cases of LDD have been reported in medical literature. Symptoms of the disease most commonly manifest in the third and fourth decades of life, although it may onset at any age. Men and women are equally affected, and there is not any apparent geographical pattern.

A variant of eccrine spiradenoma which can be multiple on the scalp and can coalesce to form a 'Turban' tumour. In pathology, a cylindroma is a tumour with nests of cells that resemble a cylinder in cross section.

Types include:

- Dermal eccrine cylindroma, a benign tumour of the skin

- Adenoid cystic carcinoma, a malignant tumour of the salivary gland

Eccrine angiomatous hamartoma usually appear as a solitary nodular lesion on the acral areas of the extremities, particularly the palms and soles.

Angiolymphoid hyperplasia with eosinophilia (also known as: "Epithelioid hemangioma," "Histiocytoid hemangioma," "Inflammatory angiomatous nodule," "Intravenous atypical vascular proliferation," "Papular angioplasia," "Inflammatory arteriovenous hemangioma," and "Pseudopyogenic granuloma") usually presents with pink to red-brown, dome-shaped, dermal papules or nodules of the head or neck, especially about the ears and on the scalp.

It, or a similar lesion, has been suggested as a feature of IgG4-related skin disease, which is the name used for skin manifestations of IgG4-related disease.

The decision to observe or treat a nevus may depend on a number of factors, including cosmetic concerns, irritative symptoms (e.g., pruritus), ulceration, infection, and concern for potential malignancy.

Large congenital nevi are caused by a mutation in the body's cells that occurs early in embryonic development, usually within the first twelve weeks of pregnancy. Mutations are sometimes found in genes that code for NRAS and KRAS proteins. There is no known method of prevention.

In dermatologic pathology, a dermal cylindroma, also dermal eccrine cylindroma or Cutaneous Cylindroma) and (less specifically) cylindroma, is a benign adnexal tumor, which occurs on the scalp and forehead.when multiple Cylindroma-Show Hat like configration.

Multiple cylindromas may grow together in a "hat-like" configuration, sometimes referred to as a turban tumor. Cylindromas are uncommon dysplasias of skin appendages.

A poroma is a benign skin tumor derived from sweat glands. Although the original term "poroma "was initially used to describe a tumor derived from the ductal epithelium of eccrine sweat glands, the term is used in general reference to tumors derived from ductal portions of both eccrine and apocrine sweat glands. Specific sub-types are primarily defined by location of tumor, and include:

- eccrine poroma

- hidroacanthoma simplex (intraepithelial poroma)

- dermal duct tumor (intradermal poroma)

- syringoacanthoma

- syringofibroadenoma

- poroid hidradenoma ("disputed as different family")

A bile duct hamartoma or biliary hamartoma, is a benign tumour-like malformation

of the liver.

They are classically associated with polycystic liver disease, as may be seen in the context of polycystic kidney disease, and represent a malformation of the liver plate.