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Basal cell carcinoma has no precursor lesion. The earliest lesions of basal cell carcinoma are generally seen as a small pink papule sometimes only 1 to 3 mm across. This papule commonly bleeds on minor trauma such as dragging a fingernail across it. This can be a useful diagnostic sign in the identification of an early basal cell carcinoma, particularly if the small papule has been present for many months and is thus obviously not a simple folliculitis.

As basal cell carcinomas grow the most common types develop the more characteristic nodularity, translucency, and telangiectasia.

There are four main clinical variants of basal cell carcinoma. These are nodular, superficial spreading, sclerosing and pigmented basal cell carcinomas.

a) Nodular Basal Cell Carcinoma

Nodular basal cell carcinoma is clinically manifested as a translucent nodule, often with telangiectatic vessels being very evident. As the nodule expands beyond 1 cm the center can begin to break down causing an ulcer surrounded by a rolled edge. The alternative name for this is "rodent ulcer".

Nodular basal cell carcinomas are common on the face, particularly along embryonal fusion planes such as the inner canthus, perinasal skin and periauricular skin. They can occur anywhere on the body that has been subject to intermittent severe sun exposure.

Childhood exposure appears to be of considerable significance, as it is for melanoma, in the development of basal cell carcinoma.

b) Superficial Spreading Basal Cell Carcinoma

Superficial spreading basal cell carcinoma is most common on the upper back. It consists of shallow plaques, pink to almost skin coloured, that slowly expand over many years. The shallowness of the lesion prevents ulceration until quite late. Typically, these lesions are very friable, and minor trauma such as dragging a fingernail across the lesion while often result in multiple pinpoint bleeding areas.

Superficial spreading basal cell carcinomas are almost all secondary to sun damage.

c) Sclerosing Basal Cell Carcinoma

Sclerosing basal cell carcinoma is often a significant diagnostic problem. The early lesion can look like a small white scar on the skin. This scar-like area slowly expands. Nodules of basal cell carcinoma can be apparent in late lesions but the sclerotic scarred area can expand to a very large size before it is clinically obvious as a skin cancer. It is most common on the face, and can produce quite significant morbidity because of its size at the time of diagnosis.

Because the margins of sclerosing basal cell carcinoma are almost always very poorly defined, it is commonly recurrent after simple surgical excision. Micrographic surgery, if available, is the surgical treatment of choice or, in patients over 60, radiation therapy with generous margins. In all cases, the lesion must be examined carefully under very good light to ascertain the approximate margins.

d) Pigmented Basal Cell Carcinoma

Pigmented basal cell carcinoma occurs in dark skinned individuals, particularly Asians. Nodular basal cell carcinomas can be pigmented, as can superficial spreading basal cell carcinomas. Nodular basal cell carcinomas that are pigmented may be confused clinically with nodular melanoma. The differentiating feature, if completely pigmented, is that there are pigment flecks around the base of the nodule that are absent in melanoma. These flecks are the engorged melanocytes. In many cases the only way to clearly differentiate is a biopsy.