PREMALIGNANT SKIN LESIONS

These type of skin lesions are not malignant but if left untreated may become malignant skin cancers. There are 2 main types of premalignant skin lesions;

Bowen's Disease (Squamous Cell Carcinoma in situ) (SCC in situ)

Bowen's Disease which is also called Squamous Cell Carcinoma in situ (SCC in situ), is a form of premalignant (precancerous) skin cancer. The term "in situ" added on the end tells us that it is a surface form of skin cancer without invasive roots and are therefore nearly always locally growing and do not spread. "Invasive" SCC’s are the type that grow inward and may spread. SCC in situ is also known as Bowen's disease after the doctor who first described it almost 100 years ago.

SCC in situ is usually a red, scaly patch. It tends to be seen on areas frequently exposed to the sun. Some itch, crust or ooze, but most have no particular feeling. SCC in situ may be mistaken for rashes, eczema, fungus or psoriasis. Sometimes they are brown and look like a sun spot or a melanoma. Because of this, a biopsy usually needs to be done to confirm the diagnosis.

If you have had an SCC in situ, you have a higher risk of other skin cancers. For this reason, you will need a regular skin exam. An untreated SCC in situ will grow larger over time and may spread out to be several cm’s across. If left untreated, some SCC’s in situ may develop into an invasive squamous cell carcinoma.

Like other forms of skin cancer, SCC in situ are mainly caused by chronic sun exposure and aging. There are two other less important causes which are unique to SCC in situ. The wart virus that causes cervical cancer (HPV 16) is often found to be infecting SCC in situ. It is thought that infection with this virus is one of the reasons why two people may have the same amount of sun damage, but only one keeps getting skin cancers. The other factor that causes SCC in situ is arsenic. Arsenic contaminated some old water wells, and was also many years ago used in some medical elixirs. People with mild Arsenic poisoning didn't die, but tended to develop cancers, both of the skin and internally.

Treatments Options

  • Creams - Are considered in patients not fit for surgery, in cosmetically sensitive areas or in areas where excision will require extensive reconstruction and/or hospitalization. These treatments are very good but the cure rates are slightly lower (75%-80%) than surgery and therefore the patient will need to be reviewed regularly to check that the lesion is cured. They usually need to be used for 4-6 weeks and irritate the area so it becomes red and scabby. It then settles over a month or two leaving minimal to no scaring
  • Photodynamic therapy (PDT) is an alternative way to "burn off" SCC in situ using a drug that is absorbed only by cancer cells. A bright light is then applied causing the release of toxins and destruction of the tumor.
  • Radiotherapy - requires multiple visits to the hospital over a 2 to 4 week period.
  • Curettage and electrodessication (scrape and burn it off). 
  •  The quickest and most successful method for removing an SCC in situ is surgical excision. The standard practice is to remove about 3mm of “normal” skin beyond the apparent edge of the lesion. It offers the highest cure rate of all treatment methods. The obvious disadvantage of surgery is that it requires an operation (pain, suffering and inconvenience) and will leave a scar. 
               

 

Lentigo Maligna (Hutchinson's Melanotic Freckle)

Hutchinson’s Melanotic Freckle was first described by Sir John Hutchinson in 1890 and therefore called Hutchinson’s Melanotic Freckle (HMF). It is now usually referred to as a Lentigo Maligna or melanoma in situ.  It usually presents in people over 40 years old, with the peak incidence is in the seventh and eighth decades.  The incidence in Australia is approximately 1.3 cases per 100,000 population.  It is premalignant i.e. not cancerous but may progress on to a malignant melanoma.  They can be present for long periods (5 –15 years) before they turn malignant although it can occur more rapidly than this.  It is not known what percentage of lesions will turn malignant.  Features suggesting malignant change include the development of slight elevation or a nodule within the lesion or increasing dark black or multiple colours within the lesion.  Typical lesions are flat with variegated colour (browns and black) and ill-defined margins. They usually occur on sun-exposed areas of the body especially the face.

Diagnosis and Treatment

The diagnosis is often suspected from clinical examination with a dermatoscope (a special magnified light).  A skin biopsy is usually required initially to confirm the diagnosis. 

Once the diagnosis has been confirmed the lesions needs to be excised with at least a 5mm margin of normal skin to minimise the risk of a melanoma developing.  On occasion it is very difficult to visualise the abnormal skin cells with the naked eye and despite a wide margin of clinically normal tissue being excised, when the tissue is processed by the laboratory, tumour extends to the margin.  If this occurs a further wider excision may then be required. 

After surgery there is a 5 to 10% chance of local recurrence therefore the area does need to have ongoing observation by the doctor and the patient.  A patient who has had a Lentigo mailgna is also at higher risk of developing further melanomas in other areas of the body and therefore needs lifelong skin examinations. 

 

 
HMF L forehead   One month after excision with 5mm margins and skin graft repair

Other therapies

Liquid nitrogen (cryosurgery), radiotherapy, cautery and topical medications (eg 5% Imiquimod cream) have all been used but have lower or uncertain cure rates.