Basal cell carcinoma of the skin is one of the commonest form of malignancy.     Visit: Epidermal tumours

It is a tumour of low degree of malignancy and is locally aggressive. This tumour is also known as "Rodent Ulcer". If the tumour is untreated it may infiltrate into the tissue and penetrate deep into the bone and cause ulceration.

Basal cell carcinoma may recur after excision. Very rarely metastasis may occur .

Basal cell carcinoma may be associated with: i) Previous scarring or trauma ;  ii) Pre-existing skin condition ; iii) Rare syndrome - Naevoid Basal Cell Carcinoma Syndrome 

Site:  May occur in any part of the body.  These tumours are usually located on the exposed parts of the body - Eg:  Face.

Tumours located at nose, ear, are difficult to treat. These lesions may recur. Large and deeply invasive tumours from the scalp, ear and sometimes from the genital region are more likely to metastasize. Some of these lesions are resistant to therapy.

Gross: Lesions may be raised or flat or ulcerated or pigmented. Flat lesions tend to be incompletely excised . The margins of flat lesions are usually less well defined.

Morphological classification based on the growth pattern and is related to the behaviour of the tumour :

1) Nodular (including micronodular ); 2)Infiltrative (including morpheic); 3) Superficial ; 4) Mixed (combination of any two or all the other types).

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NODULAR:   Commonest type:  About 50% of cases show this pattern.

Clinical appearance:  Rounded or polypoid or nodular appearance.

Arrangement of cells:   Tumour grow in rounded masses in the dermis and may show any of the following features-  i) Solid pattern  ; ii)  With central necrosis  iii) Degeneration with cyst or microcyst formation.

Peripheral palisading of nuclei is prominent ; There is surrounding retraction artifact.

Cellular character : Small darkly stained with with scanty cytoplasm ; Variable degree of differentiation.

Stroma :  Loose and myxoid.

Subgroup: 15% cases show micronodular basal cell carcinoma - The lesion consists of small nodules which are usually less than 0.15mm in diameter .

INFILTRATIVE: The groups of cells in the dermis are of varying size with irregular outline and pointed spiky projections. The larger groups are located centrally and superficially. Palisading is poorly developed.

Often there are small groups of cells at the periphery . These cells infiltrate between collagen bundles in the dermis.

Stroma is less myxoid.

Subgroup:  Morpheic type-  Small, irregular islands and cords of cells infiltrating into the dense sclerotic fibrous stroma.

SUPERFICIAL (APPARENTLY MULTIFOCAL ):  There are small buds of proliferating basal cells protruding from the epidermis into the superficial dermis.  The intervening epidermis is normal. There is a diffuse inflammatory cellular infiltrate in the dermis.  The lesions are common on the trunk and limbs.

Superficial and infiltrative patterns may be found at either the lateral or deep margins.  These lesions are likely to be incompletely excised.

MIXED:   In some cases together with superficial basal cell carcinoma there are isolated groups of basal cells in the reticular dermis, these are termed as mixed type.

Significance of morphological classification: Local recurrence is more common in the infiltrative, micronodular and superficial mutifocal types of basal cell carcinoma. Infiltrative and micronodular forms are more likely to occur in incompletely excised tumour, with lesions extending to the margins of excision. As infiltrative pattern is found in recurrent and deeply invasive tumours, this form is generally regarded as more aggressive.

Classification according to histopathological features: Microscopically innumerable features have been describe. These features have been used for classification.  Some of these types have been briefly described:

 Basosquamous carcinoma:   3 cell types: i)Basaloid cells ii)Squamoid cells iii) Intermediate cells. Aggressive lesion.  Unlike squamous cell carcinoma, in Basosquamous carcinoma BerEP4 is positive.

 Fibroepithelioma:  This is a rare type of lesion. The basal cells grow from the surface, forming a network.

Organoid differentiation: Follicular differentiation has to be differentiated trichoepithelioma.  Sebaceous differentiation must be distinguished from sebaceous tumours. Sweat gland or duct differentiation must be distinguished from sweat gland tumours. Matricial differentiation has been also been reported characterized shadow cells as seen in Pilomatrixoma.

Infundibulocystic : Anastomosing nests of cells together with small infundibular cyst-like structures containing keratinous material.

Pigmented: Proliferation of melanocytes in the tumour and presence of melanophages in the stroma.

Keratotic: Nests and islands of basaloid cells with peripheral palisading together with squamous differentiation and keratinization.

Metatypical type: Basal cell carcinoma consisting of nests and strands of cells maturing into larger and paler cells. Peripheral palisading is usually not present.

Other rare features in basal cell carcinoma include presence of granular cells, clear cells (Image Link1; ImageLink2) , signet ring cells and giant tumour cells.

Nevoid Basal Cell Carcinoma Syndrome: It is an autosomal-dominant disorder characterized by multiple basal cell carcinomas, jaw cysts, palmar/plantar pits, calcification of the falx cerebri, and spine and rib anomalies.