Keratoacanthoma :

 rapidly growing, 1 to 2 cm dome-shaped skin tumor with a centralized keratinous plug

 Subtypes : solitary keratoacanthoma, subungual keratoacanthoma, mucosal
keratoacanthoma, giant keratoacanthoma, keratoacanthoma centrifugum marginatum,
generalized eruptive keratoacanthoma of Grzybowski, and multiple keratoacanthomas
Ferguson-Smith syndrome
 Etiology : ultraviolet (UV) radiation, exposure to chemical carcinogens, immunosuppression,
use of BRAF inhibitors, genetic predisposition including mutations of p53 or H-Ras, viral
exposure including human papillomavirus (HPV), and recent trauma or surgery to the
location
 Epidemiology : all age groups although, rarely before the age of 20. The peak incidence of
solitary keratoacanthoma is between 50 and 69 years of age. They occur more frequently in
men with a male to female ratio of 2:1. The majority have been described in fair skin
individuals with the highest rates found in those with Fitzpatrick I-III classification. more
frequent in immunosuppressed individuals and are more locally invasive.
 Most occur on sun-exposed hair-baring areas with the face, head, neck, and dorsum of
extremities. Lesions on the trunk are uncommon. Lesions begin as a small, round pink or
skin-colored, papule that undergoes rapid growth to a dome-shaped nodule with a central
keratin plug giving it a crateriform appearance. The classic size is 1 to 2 cm. It should be
noted that keratoacanthoma may be seen in areas without sun exposure including the
mucosal surfaces, subungual areas, buttocks, and anus. Physical examination should include
regional lymph node examination due to the chance of invasion and metastases.
 Histopathology: circumscribed proliferation of well-differentiated keratinocytes. This has
been described as multilobular exophytic or endophytic cyst-like invagination of the
epidermis. The epidermis extends over the tumor, and there is a central horn plug of keratin.
Peripheral to the keratin-filled crater are lip-like, peripheral borders of the epidermis.
Intraepidermal neutrophilic abscesses are visualized in addition to horn pearls. The cells of
the keratoacanthoma tumor are enlarged and atypical keratinocytes. They have a cytoplasm
described as eosinophilic. Due to 3 stages of solitary keratoacanthoma, the histological
examination can vary between stages. In comparison to squamous cell carcinoma,
keratoacanthoma has intraepidermal microabscesses and tissue eosinophilia more
commonly found. Recently keratoacanthoma has been reclassified as squamous cell
carcinoma keratoacanthoma type (SCC-KA).
 Dermoscopy  cannot reliably distinguish between keratoacanthoma and squamous cell
carcinoma; however, it can be used to distinguish both from other raised non-pigmented
skin lesions. In particular, blood spots, white circles, and keratin are useful clues for
distinguishing the lesion. White circles had the highest specificity.
SQUAMOUS CELL CARCINOMA:
 Second most common skin cancer (BCC no 1)
 Ultraviolet (UV) solar radiation is the primary risk factor
 ratio of squamous cell carcinoma to basal cell carcinoma incidence of 3:1 has been reported,
but more recent studies suggest that the ratio may be closer to 1:1. Furthermore, it has been
reported that, with increasing age, the ratio trends toward squamous cell carcinoma
occurrence. Squamous cell carcinoma most commonly appears after the age of 50 in areas of
past sun exposure, and typically occurs in males with light skin and light eyes who have a
history of UV solar radiation exposure. very prevalent in patients that are
immunosuppressed
 The most common areas for squamous cell carcinoma to occur are the face, neck, bald scalp,
extensor forearms, dorsal hands, and shins. The color varies from flesh toned to
erythematous with variable degrees of scale, crusting, ulceration, and hyperkeratosis.
Occasionally, telangiectases with or without active bleeding may be present. Squamous cell
carcinoma can be flat, nodular, and even plaque-like in some cases with significant
induration and/or subcutaneous spread noticeable on palpation. Squamous cell carcinoma
can occasionally be painful and tender, and these may be signs of perineural invasion.
 Histopathologically, squamous cell carcinoma is notable for irregular nests, cords and sheets
of neoplastic keratinocytes invading the dermis. Lesion thickness is of particular importance
when predicting risk for metastasis with a thickness more than 4 mm associated with a
higher risk. Immunoperoxidase staining for cytokeratins 5/6/AE1/AE3 is useful in situations
where the diagnosis is in question, especially with poorly differentiated squamous cell
carcinoma
BASAL CELL CARCINOMA:

 Basal cell carcinoma is the most common cutaneous malignancy

 mostly arises on sun-damaged skin and rarely develops on the mucous membranes or palms
and soles. Basal cell carcinoma is usually a slow-growing tumor for which metastases are
rare
 BCC usually appears as flesh- or pink-colored, pearly papules with overlying ulceration or
telangiectatic vessels
 BCC occurs on the head or neck in the majority of cases, but can involve the trunk and
extremities
 types include: nodular, micronodular, superficial, morpheaform, infiltrative and
fibroepithelial (also known as fibroepithelioma of Pinkus). Combinations of these types can
occur as well. The majority of BCCs are amelanotic, but variable amounts of melanin may be
present within these tumors.
 Ultraviolet light exposure is not the only risk factor as 20% of BCC arise on non–sun-exposed
skin. BCCs also occur due to various other factors such as ionizing radiation exposure, arsenic
exposure, immunosuppression, and genetic predisposition
 Men generally have higher rates of BCC than women. BCC is more frequent in geographic
locations with greater UV exposure, such as those at higher or lower latitudes. The most
common predictor of BCC development is a history of squamous cell carcinoma (SCC) or
BCC. Patients are at least ten times more likely to develop a second BCC if they have a BCC
history compared to patients without a history of non-melanoma skin cancer. Over the last
30 years, estimated incidence rates have risen between 20% and 80%. Incidence rates for
BCC also increase with age, with the median age of diagnosis being 68 years.
 Histo : The characteristic feature seen in BCCs is islands or nests of basaloid cells, with cells
palisading at the periphery in a haphazard arrangement in the centers of the islands. Each of
these small pleomorphic cells is composed of a basophilic nucleus without a discernible
nucleolus and scanty cytoplasm. Retraction artifact, also referred to as clefting, is usually is
seen between the tumor and its surrounding stroma on paraffin-embedded sections. Mucin
deposition may be present within the tumor and in the stroma around the tumor. Mitotic
figures also may be present. Perineural growth, also known to as perineural invasion, can be
an indicator of aggressive disease.
 The histologic differential diagnosis may include trichoepithelioma or trichoblastoma.
 Many clinical variants of BCC exist, but the most recognized types are superficial, nodular,
and morphea-like BCC. Nodular BCC is the most common.
 BCC typically presents as a shiny, pink- or flesh-colored papule or nodule with surface
telangiectasia. The tumor may enlarge and ulcerate, giving the borders a rolled or rodent
ulcer appearance. The most common sites for nodular basal cells are the face, especially the
nose, cheeks, forehead, nasolabial folds, and eyelids. Patients often give a history of crusting
and recurrent bleeding, causing them to seek evaluation. Pigmented nodular BCCs are more
common in dark-skinned individuals.
 Superficial BCCs present as a pink-red, scaly, macule or patch, which may contain
telangiectasia. They have a predilection for the shoulders, chest, or back, and multiple
lesions may be present. There are also pigmented variants of superficial BCC. Clinically,
superficial BCC can appear similar to inflammatory dermatoses such as eczema or psoriasis,
 so one should consider the diagnosis of superficial BCC when faced with a persistent,
erythematous, scaly plaque. Portions of superficial basal cell carcinomas can evolve into
nodular BCC over time.
 The other common clinical variant of BCC is the morpheaform subtype. This tumor
frequently presents as white- or flesh-colored with areas of induration and ill-defined
borders. Morpheaform BCCs may resemble a scar or plaque of morphea. The lesion's surface
is typically smooth, although crusts with underlying erosions or ulcerations, as well as
superimposed papules, may be observed. Telangiectasias also may be present. The biologic
behavior is usually more aggressive, with extensive local destruction.