Tumours and cysts of the skin
The skin has many functions, including the provision of a physical barrier between the body and the environment, and temperature regulation. The skin structure, of epithelium and appendages with the underlying dermis, forms a complex and interactive grouping of tissues and cells to serve these functions. It is not surprising that genetically determined processes and external factors can interact to produce lesions that by their superficial placement are both obvious and deserving of attention. The common lesions of the skin of importance in relation to possible surgical therapy will be dealt with under the headings of cysts, benign tumours, malignant lesions and malignant tumours.
Cysts of the skin
These are common lesions whose only importance is their cosmetic effect and their propensity to become infected.
Epidermal or epidermoid cysts
Epidermal or epidermoid cysts are the most common cysts, and are frequently misnamed sebaceous cysts in the mistaken belief that they arise from sebaceous glands. True sebaceous cysts do occur but are rare. Epidermal cysts are in fact inclusion cysts lined by fully differentiated epidermis. They are filled by laminated keratin, which forms the characteristic, white, unpleasant-smelling content. They occur most commonly on the face, the scalp, the back and the scrotum and may be shelled out under local anaesthesia if uninfected or indeed enucleated through small incisions to provide optimal cosmetic results. Infected cysts should be treated by incision and drainage, with later excision to avoid recurrence.
Milia are tiny multiple epidermal cysts that occur on the face, particularly around the eyes, and can be shelled out for cosmesis.
Dermoid cysts are congenital inclusion cysts that occur at points of fusion, particularly in the face. Their structure differs from epidermal cysts in that they show multiple skin appendages rather than epidermis alone. They can be treated by excision but are less readily enucleated than epidermal cysts.
Post-traumatic dermoid cysts result from implantation of epidermis and appendages under the skin surface by penetrating injury and are most common in the hands and fingers. Such cysts are often densely adherent to the underlying dermis but are readily excised.
Benign epidermal tumours
These are extremely common and arise from the epidermis itself, or more rarely from the skin appendages.
Seborrhoeic keratoses are the most common of these lesions and occur on the trunk or limbs of the middleaged or elderly. They develop initially as flat plaques with a waxy surface that progressively thickens, often with pigmentation due to haemosiderin deposition. Exuberant keratin and parakeratin production results from simple proliferation of keratinocytes for unknown cause, without any dermal involvement, so that the lesions are said to have a ‘painted on’ appearance. Their protruding nature means that the lesions can be traumatised, with subsequent low-grade infection. Such keratoses can be removed under local anaesthesia for this reason or for cosmesis.
Actinic keratosis represents a progressive dysplastic change in the epidermis and the underlying dermis as the result of exposure to UV light. There is a build-up of excessive keratin and parakeratin, while the underlying dermis contains thickened elastic fibres (elastosis) produced by damaged fibroblasts. The lesions occur most commonly on exposed areas, such as the ears in the male, or the nose and the backs of the hands and forearms. They appear as rough crusty areas of thickening that may bleed when traumatised. Actinic keratoses are unquestionably premalignant, in contradistinction to seborrhoeic keratosis. They can be managed by the application of cytotoxic creams or by surgical excision if there is any suspicion that malignant change has already occurred.
Kerato-acanthoma is a benign lesion that presents on the cheek, nose, ear or back of the hand in the elderly as a rapidly growing nodule which develops a characteristic central keratin plug. The lesions usually develop to several centimetres in diameter over the course of a few weeks and regress spontaneously and rapidly. They can thus be treated expectantly.
Kerato-acanthomas may occur in patients receiving immunosuppression, such as transplant recipients, and in these circumstances should be treated as squamous carcinoma because they may behave aggressively.
Malignant epithelial tumours
The most common tumours arise from the cells of the epidermis in the form of basal and squamous carcinomas and melanoma, which will be considered with pigmented lesions.
Basal cell carcinoma
Basal cell carcinoma (BCC) is the most common form of skin cancer and occurs almost exclusively in sunexposed areas of the skin, in the adult white population over the age of 40 years. They are rare in the oriental population and almost never occur in black-skinned races.
Between 75 and 80% of the lesions occur in the head and neck, usually above a line running from the corner of the mouth to the ear, with the remainder being situated on the limbs and a minority on the trunk. Although the cell of origin was presumed to be the basal cell in the epidermis, it is probable that the true progenitor is a potential epithelial cell in pylosebaceous tissue. Exposure to UVB is believed to be the precipitating factor, and there is no clear genetic basis for the disease apart from race, except in some rare conditions such as the naevoid BCC syndrome, where BCC occurs in childhood, often in non-sun-exposed areas and with associated odontogenic cysts of the mandible, medulloblastoma and tumours of the reproductive organs.
Basal cell carcinoma presents in a wide variety of forms, but the most common is as a waxy translucent nodule with a thin overlying epithelium and a fine network of vessels traversing the margins, probably the result of tumour-induced angiogenesis. Central regression may lead to depressions in the centre of the lesion, which may progress to ulceration to show the classical ‘rodent ulcer’ appearance. The tumours may be multifocal and as they grow tend to become infiltrative and may involve deeper tissues. They may thus become locally aggressive but they do not metastasise except in very rare instances.
Optimal treatment for nodular BCC depends on size. Lesions less than 1 cm in diameter are rarely deeply invasive and can be treated by electro-desiccation with curettage, by cryosurgery or by excision with a narrow margin in terms of depth and width. Radiotherapy is an alternative form of therapy but not in areas close to cartilage. Lesions greater than 1 cm in size are best treated by excision with peroperative confirmation of the margins of excision, which should not be less than 1 mm.
If treatment has been adequate, recurrence is rare, except in the case of sclerosing BCC, which may require multiple procedures to achieve control.
Squamous cell carcinoma
Squamous cell carcinoma (SCC) is the second most common tumour of the skin. The major aetiological factor is again exposure to UV light. Although such lesions are most commonly seen in the elderly, they are now becoming increasingly frequent in young adults because of excessive sun exposure in childhood. As expected from its aetiology, the lesions are most common in white populations and are seen most frequently on the face and ears, lip, the back of hands and forearms.
Clinical presentation is initially as an area of crusting that is clinically indistinguishable from solar keratosis but which on excision shows the cellular atypia that provides the diagnosis of carcinoma in situ before the breaching of the basement membrane at the dermoepidermal surface to form frank invasive carcinoma. If the lesions are untreated at this stage, they will progress to form a nodule or plaque that is irregular in shape and may ulcerate with a pink rolled edge. Unlike BCC, SCC can metastasise, usually to the regional lymph nodes but also systemically, although this is unusual unless the lesions are large or neglected. It should be noted that immunosuppression is associated with a much higher incidence of SCC, as for example in renal transplant recipients in whom the normal 4 : 1 ratio of BCC to SCC is reversed; BCC are also more common in such patients than in the normal age- and sex-matched population.
Treatment of SCC is primarily surgical with excision to a margin of at least 0.5 cm in depth and laterally, as determined on clinical grounds, although this margin may be reduced in the head and neck because of cosmetic problems. If lesser margins are used, frozen section should be utilised to ensure that complete excision of the lesion has occurred. Tumour thickness is closely related to outcome. Local recurrence is unusual with lesions less than 4 mm in thickness and metastasis is more common in lesions which are greater than 10 mm in thickness (Table 42, “Excision margins related to tumour thickness”). Adjuvant radiotherapy is only used when the margins of excision are compromised by vital structures. Radiotherapy as a primary treatment is almost as effective as surgery but should be reserved for those patients not fit for surgery. As nodal involvement with cutaneous SCC is unusual, prophylactic lymph node dissection is not used and therapeutic dissection is only indicated when there are enlarged glands that prove on biopsy to demonstrate involvement with tumour. Prognosis is good, with at least 95% disease-free survival at 5 years. Local recurrence is rare as long as surgical excision has been adequate in the first instance.
|melanoma||Stage (TNM)||Excision margin|
|In situ||pTis||5 mm|
|<1.5 mm||pT1, pT2||1 cm|
|>4 mm||pT4||2–3 cm|
Pigmented tumours of the skin are common. Their major importance is the propensity of some lesions to progress to the formation of melanoma, or the initial clinical differentiation from primary melanoma. A number of lesions that may become pigmented, such as seborrhoeic keratoses or basal cell carcinoma, have been dealt with previously.
The term naevus should refer by definition to any congenital lesion of the skin, but by convention is used to describe any congenital or acquired neoplasm of melanocytes.
Acquired or naevo-cellular naevi are common. An Australian survey demonstrated 15 such lesions per person in an adult white Caucasian population. They are most common in sun-exposed areas of the body. They are formed by melanocytes that have been transferred from their usual dendritic single-cell position among the basal layers of keratinocytes to form aggregates along the dermo-epithelial junction. This aggregation of cells forms a junctional naevus. The cells of such naevi show little individual change, and mitotic figures are not numerous.
The clinical appearance of each form of naevus is thus important, although it must be understood that clinical interpretation of any skin lesion is not always accurate and such lesions must be subjected to excisional biopsy if there is any uncertainty about their nature. The junctional naevus is impalpable, pale to dark brown in colour and is usually small, rarely being more than 1 cm in diameter. They may appear in childhood but usually become obvious around puberty, growing slowly until the cessation of skeletal growth in late adolescence. In contrast, compound naevi are palpable, because of the size of the collection in the papillary dermis. These naevi are usually darker in colour than junctional naevi. The transitional phase between junctional and compound naevus means that some lesions show the characteristics of both.
Dysplastic naevus (DN)
Dysplastic naevi (BK-moles) occur as large (greater than 5 mm in diameter) flat macules or slightly raised plaques that are present in large numbers all over the body surface but with a particular concentration on the trunk. These naevi, in contrast to the naevi already described, are frequent in non-sun-exposed areas. They commonly have an irregular contour and variable colour, particularly being darker in the centre than on the periphery. Histologically, there is replacement of the normal basal cell layer of the epidermis by naevus cells at the dermo-epithelial junction with elongation of rete ridges. In the majority of cases there is a strong family history of such naevi and sometimes an additional family history of melanoma. Where there is an established family history of melanoma in association with DN, the trait is inherited in an autosomal dominant fashion. DN may be a pleiotrophic manifestation of the Ip36 familial melanoma gene, designated CMM1.
The management of such patients requires excisional biopsy of a typical lesion to establish the diagnosis, with genetic studies where appropriate and regular review with photographs and measurement of lesions for comparison, allowing excision of suspicious lesions at an early stage. Where there is no family history of melanoma, there is a much lesser chance of development of melanoma, and review can be less intense.
Juvenile naevus (Spitz naevus) is most common in children and adolescents but may also occur in adults. It presents as a pink nodule that rapidly increases in size and on excision shows frequent mitoses and cellular pleomorphism which may raise questions of malignancy. Melanoma is comparatively rare in children and it is probable that some cases reported in the past have actually been Spitz naevi, which appear to have no malignant potential. However, this is not to say that melanoma does not occur in children. Indeed when it does occur it may be aggressive in its behaviour and have a poor prognosis.
Aetiology and pathology
Melanomas are made up of malignant cells arising from melanocytes in the skin but can also arise in oral and anogenital mucosa, and in the eye.
Cutaneous melanomas, like naevo-cellular naevi, are a disorder of white-skinned Caucasian populations, with the highest incidence being in white populations living close to the equator who are exposed to UV light during both work and recreation. There has been a rapidly increasing incidence in such populations, and even in susceptible populations in Northern Europe with a much lower regular exposure to sunlight. It is probable that this is a real increase in incidence rather than a process of earlier detection, although public education programmes now lead to much earlier presentation of the disease. The role of UV light is well established, with melanoma being most common in sun-exposed skin such as that of the upper back in males and females and also in the lower leg in females.
Melanoma can be classified into four types: lentigo maligna, superficial spreading, nodular, and acral lentiginous. As noted previously, a melanoma gene has been mapped to chromosome Ip36, and a second, designated CMM2, to chromosome 9p21, with the cell cycle regulator CDKN2A as the candidate gene.
Lentigo maligna occurs in elderly patients, usually more than 70 years of age, and is more common in men than in women. It appears as an extensive melanotic lesion (Hutchinson's melanotic freckle) on the cheek or temple. It is characteristically dark brown in colour and develops over many years as a superficial impalpable lesion unless malignant change occurs. Malignant change is manifested by the development of palpable darker nodules within an irregular edge, and this change is often multicentric. Hutchinson's freckle itself requires no specific treatment apart from regular observation, but lesions demonstrating suspicious changes should be removed by excisional biopsy. If malignant on biopsy, the entire lesion should be widely excised. Prognosis is good, with at least 95% disease-free survival at 10 years. There is a tendency for lateral and superficial spread of tumours long before vertical invasion occurs.
Superficial spreading melanoma
Superficial spreading melanoma is the most common form of melanoma and can occur in any site and at any age, although it is most common in middle age and commonly arises from a pre-existing naevus as already discussed. Characteristically, it is slightly raised above the skin surface, is variegated in colour (often with a dark brown or even black component) and has an irregular edge. Over a variable period, the lesion remains within the epidermis and then involves the reticular dermis. It is rare for metastasis to occur at this phase of radial growth. If untreated, an invasive vertical growth phase supervenes, with progressive involvement of the deeper dermis and underlying tissues and the development of metastatic potential. It is now possible to use a variety of melanoma antigens to discriminate between benign melanotic lesions, in situ melanoma, the radial and vertical growth phases of invasive melanoma, and finally metastatic melanoma. These tests give clear indications of differences in cell behaviour at these various phases.
The treatment for superficial spreading melanoma is excisional biopsy with a margin that varies with the size of the primary lesion and subsequent assessment of depth of invasion. This is determined by the use of Clark's levels of invasion, which define six levels in terms of the anatomy of the epidermis and dermis, or by the thickness of the lesion, as described by Breslow. Although Clark's levels have some correlation with prognosis it is clear that the simple measurement of the thickness of the lesion gives an even better correlation. For those with a thickness of less than 0.75 mm, 95% 10-year survival can be expected. This contrasts with only 25% survival at 10 years if the thickness is greater than 4 mm. There has been much controversy about the margins of excision in the past. It had been felt that radical excision with at least a 5-cm margin was necessary for all melanomas, but it is clear that with superficial spreading melanoma, a limited margin is quite adequate.
There is also controversy about the role of elective lymph node dissection (ELND). On present evidence, as nodal metastasis is rare in lesions less than 1 mm in thick, ELND should not be performed in such cases. As patients with invasive lesions more than 4 mm thick are unlikely to survive in any event, the operation is superfluous.
Of particular interest has been the development of lymphotic mapping following intradermal injection of radiolabelled colloids around the primary site, with removal of “sentinel nodes” and histological and histochemical examination with subsequent full node dissection if positive. This procedure is being examined in a large multicentre, international trial and is not standard therapy.
Nodular melanoma presents as its name suggests with a protruding lesion usually arising from a pre-existing naevus, the nodular form being one component of vertical invasion. The nodule may be dark or may be amelanotic. As it is really a particular form of invasive melanoma, it is treated on its merits in terms of thickness by wide local excision with consideration of TLND and adjuvant therapy.
Acral lentiginous melanoma
Acral lentiginous melanoma occurs in all races in nonpigmented areas, such as the palms of the hands, the soles of the feet, the subungual area and on mucous surfaces. They are often pink in colour with little in the way of pigmentation, and there is often delay in diagnosis because of this non-specific appearance. Treatment is as for superficial spreading melanoma, depending on the thickness of the lesion. Late presentation often means that there is a significant invasive element, and wide excision with or without adjuvant therapy may be necessary.
The benefits of combining surgery with adjuvant chemotherapy are now clear in relation to some cancers. This is undertaken in the belief that metastasis will often have occurred before patients present for primary surgery, although this may not be clinically apparent, and that systemic therapy is most likely to be effective in such patients when the bulk of tumour has been removed by surgery and the residual tumour burden is low.
For melanoma of poor prognosis confined to a limb, an additional form of treatment aimed at controlling presumed intransit metastasis is perfusion of the isolated limb at high temperatures through an oxygenated circuit that contains phenylalanine mustard, which is selectively taken up by melanoma cells (at least in theory). The role of isolated limb perfusion (ILP) as an adjuvant to surgical treatment in primary treatment remains unclear until the results of a number of current randomised controlled trials are available.
Radiation therapy has no role as an adjuvant to surgery for localised disease that is treatable by wide excision, but it is of value in the treatment of recurrent or inoperable disease with effective local control, particularly of nodal metastases.