Squamous Cell Skin Cancer

Squamous cell carcinoma (SCC) is the second most common form of skin cancer and
accounts for 20% of skin cancers. Squamous cell carcinoma frequently arises on the
sun-exposed skin of middle-aged and elderly individuals.

Most squamous cell carcinomas are readily identified and removed in the physician's
office as a minor surgical procedure. Larger and more invasive lesions may require
aggressive surgical management, radiation therapy, or both. High-risk squamous cell
carcinoma carries a significant risk of metastasis and, as such, requires careful
evaluation and treatment.

General risk factors associated with the development of squamous cell carcinoma are
as follows:
  • Age older than 50 years
  • Male sex
  • Light skin; blonde or light brown hair; green, blue, or gray eyes
  • Skin that sunburns easily (Fitzpatrick skin types I and II)
  • Geography (closer to the equator)
  • History of prior nonmelanoma skin cancer
  • Exposure to UV light (high cumulative dose of sunshine, tanning beds, or
    medical UV treatments)
  • Exposure to chemical carcinogens (eg, arsenic, tar)
  • Exposure to ionizing radiation (medical treatments, occupational or accidental
    radiation exposure)
  • Chronic immunosuppression
  • Chronic scarring conditions
  • Certain genodermatoses
  • Human papillomavirus (HPV) infection (specific subtypes)

Pathophysiology
Squamous cell carcinoma is a malignant tumor of epidermal keratinocytes. Most
squamous cell carcinomas arise from sun-induced precancerous lesions known as
actinic keratoses (AKs). Patients with multiple AKs are at increased risk for developing
squamous cell carcinoma.  Squamous cell carcinoma is capable of locally infiltrative
growth, spread to regional lymph nodes, and distant metastasis, most often to the
lungs, brain, and liver.

Mortality/Morbidity
The majority of squamous cell carcinomas are readily treated by surgeons in their
offices, and produce few sequelae.  A subset of high-risk tumors causes most of the
morbidity and the mortality associated with squamous cell carcinoma. Such tumors
may cause extensive destruction of local tissue, and their removal may create a
substantial cosmetic deformity.

The overall risk of metastasis for squamous cell carcinoma is in the range of 2-6%.  
Lymph node metastasis is associated with significant morbidity; however, 5-year
survival rates as high as 73% have been achieved with the combination of surgical
lymphadenectomy and radiation therapy. Once lung, brain, or liver metastasis occurs
the disease is virtually incurable.

Race
Squamous cell carcinoma is the second leading cause of skin cancer in whites.  
Persons of Irish or Scottish ancestry have the highest prevalence in the United
States. Squamous cell carcinoma is relatively rare in people of African and Asian
descent, although it is the most common form of skin cancer in these groups.
Squamous cell carcinoma in blacks carries a higher mortality rate, perhaps due to
delayed diagnosis because tumors are more likely to occur in sun-protected areas,
including the scalp and sites of previous injury and scarring.

Sex
Squamous cell carcinoma occurs in men 2-3 times more frequently than it does in
women, most likely as a result of greater cumulative lifetime UV exposure.

Age
The typical age at presentation is approximately 70 years; however, this varies
widely, and, in certain high-risk groups (eg, organ transplant recipients [OTRs],
patients with epidermolysis bullosa), squamous cell carcinoma often manifests at a
much younger age.

Clinical History
A detailed patient history often reveals the presence of one or more risk factors for
squamous cell carcinoma (SCC). Most squamous cell carcinomas are discovered by
patients and are brought to a physician's attention by the patient or a relative. The
typical squamous cell carcinoma manifests as a new or enlarging lesion that concerns
the patient. Squamous cell carcinoma is typically a slow-growing malignancy, but
some lesions enlarge rapidly. Although most squamous cell carcinoma patients are
asymptomatic, symptoms such as bleeding, weeping, pain, or tenderness may be
noted, especially with larger tumors. Numbness, tingling, or muscle weakness may
reflect underlying perineural involvement, and this history finding is important to elicit
because it is associated with a very poor prognosis.

Physical Finding
Typical squamous cell carcinoma tumor: The characteristic invasive squamous cell
carcinoma is a raised, firm, pink-to-flesh–colored keratotic papule or plaque arising on
sun-exposed skin.  Approximately 70% of all squamous cell carcinomas occur on the
head and neck, with an additional 15% found on the upper extremities. Surface
changes may include scaling, ulceration, crusting, or the presence of a cutaneous
horn.  Less commonly, squamous cell carcinoma may manifest as a pink cutaneous
nodule without overlying surface changes.  A background of severely sun-damaged
skin, including solar elastosis, mottled dyspigmentation, telangiectasia, and multiple
AKs, is often noted.

Lymphadenopathy: With any invasive (not in situ) squamous cell carcinoma, regional
lymph nodes should be examined. Lymph node enlargement must be further
evaluated by fine-needle aspiration (FNA) or nodal biopsy.  A complete metastatic
work-up is warranted if the FNA is positive.

Major Causative Factors
Sun Exposure: The most common type of squamous cell carcinoma is the sun-induced
type. A history of long-term sun exposure dating back to childhood is frequently
elicited. Many patients report having experienced multiple blistering sunburns during
their lifetime, while others may have used indoor tanning beds or received UV light
therapy (eg, psoralen plus UVA [PUVA] for psoriasis).  

UV sunlight exposure: The component of sunlight believed to be most important in
cutaneous carcinogenesis is UVB (290-320 nm), which is both an initiator and a
promoter of carcinogenesis.  UVB-induced photocarcinogenesis appears to work by
suppressing the immune system in several ways. The UVB spectrum inhibits antigen
presentation, induces the release of immunosuppressive cytokines, and elicits DNA
damage.

Fair complexion: Individuals with Fitzpatrick skin types I and II account for most of the
patients who develop squamous cell carcinoma.

Immune suppression: Patients should always be questioned about possible sources
of immunosuppression. A history of solid-organ transplantation, hematologic
malignancy (particularly chronic lymphocytic leukemia [CLL]), HIV infection or AIDS, or
long-term use of immunosuppressive medications (eg, as treatment for an
autoimmune condition) may be elicited.

Marjolin ulcer: This eponym refers to a squamous cell carcinoma that arises from
chronically scarred or inflamed skin. Patients may report a change in the skin (eg,
induration, elevation, ulceration, weeping) at the site of a preexisting scar or ulcer.
The latency period is often 20-30 years; therefore, the diagnosis requires a high
index of clinical suspicion.

HPV-associated squamous cell carcinoma: Virally induced squamous cell carcinoma most
commonly manifests as a new or enlarging warty growth on the penis, vulva, perianal
area, or periungual region. Patients often present with a history of "warts" that have
been refractory to various treatment modalities in the past. A history of previously
documented genital HPV infection is common.

Chemical carcinogens: Exposure to arsenic is a well-established cause of cutaneous
squamous cell carcinoma and internal cancers. Today, the main source of arsenic is
contaminated well water, although arsenic may also be found in traditional Chinese
medicines. Other carcinogens associated with squamous cell carcinoma include
polycyclic aromatic hydrocarbons such as tar, soot, and pitch.  Police and firefighters
are a high risk group for this causation related cancer.

Iatrogenic immunosuppression: The use of immunosuppressive medications to prevent
rejection in OTRs is associated with a 65- to 250-fold increased risk of developing
squamous cell carcinoma compared with the general population.  The primary risk
factor in these patients is cumulative lifetime UV exposure in combination with having
skin type I or II. This risk also increases with the number of years
posttransplantation, presumably because of the cumulative effects of prolonged
immunosuppressive therapy.  The greatest risk occurs in heart transplant patients,
with diminishing risk seen in recipients of kidney and liver transplants, which
correlates with the degree of immunosuppression (ie, number and/or dosage of
medications) typically required to prevent rejection in these patient populations.

Chronic inflammation: Chronic inflammation, irrespective of the underlying etiology,
may lead to the development of squamous cell carcinoma. Both noninfectious
inflammatory diseases and chronic infections have been associated with squamous
cell carcinoma.

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