Cutaneous Neoplasms

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Agricultural occupational skin cancers are malignancies that result from exposure to carcinogenic forces present in agriculture. Of all occupational cancers, 75% are skin cancers, and 60% of those are basal cell carcinomas (BCCs), 34% are squamous cell carcinomas (SCCs), and 6% are mixed. Actinic keratoses (AKs) are precancerous lesions caused by excessive sun exposure. Melanomas may occur but typically appear in older persons, and their exact rate in agriculture is unknown. In Finland, lip cancer (BCC and SCC) is extremely common but cancers of the head aren't, presumably due to wearing hats (Table 18.6) (1,8,9,37,41,42).

Causes of Agricultural Skin Cancers

Fair skin, blond hair, and blue eyes predispose to the appearance of skin cancers in Caucasian people. The elevated levels of melanin in dark-skinned people offer an incomplete protective effect. The most common types of cancer that affect the Caucasian population are BCC and SCC (43). There are five recognized causes of agricultural skin cancers:

1. Chemical carcinogens

2. Cocarcinogens or promoters

3. Physical carcinogens

4. Ionizing radiation

5. Nonionizing radiation (41,43,44)

Chemical Carcinogens

Coal-tar, mineral oils, pitch, soot, and asphalt are common chemical carcinogens. Chemicals that contain 4- to 5-ring aromatic hydrocarbons such as benzene and pyrene are potent carcinogens. Arsenic used in sheep dip has caused skin cancer in sheepherders. Used as a wood preservative for vine trellises in some parts of the world, arsenic can cause skin cancer in vineyard workers (1,41).

Table 18.6. Diagnostic findings in agricultural skin cancers.

Type of tumor

Location

Color

Morphology

Metastasis

Treatment

Basal cell

Chronically

Pearly gray

Circumscribed

Slow but

Cryotherapy

carcinoma

sun-

or slightly

relentless

Curettage

(BCC)

exposed

diffuse

growth,

and

areas

Morpheaform,

rarely

electro-

nodular,

metastases

desiccation

infiltrating,

excision

or superficial

(Mohs'

surgery)

Squamous

1. Sun

Erythemic

Keratotic

Slow and

Same

cell

exposed.

papule or

relentless,

carcinoma

2. Secondary

nodule that

metastasis

(SCC)

to scarring

may ulcerate

occurs

Process

Actinic

Pale sun-

White

Rough scaly,

Doesn't

Topical

keratosis

exposed

keratin

usually

metastasize,

5-fluorouracil

(AK)

skin

<less than

can evolve

Cryotherapy

>1cm

into BCC

Curettage

Electro-

desiccation

Dermabrasion

Laser

resurfacing

Melanomas

Sun-exposed

Variable,

Asymmetric

Wide excision

skin,

dark

lesions,

(Mohs)

history of

brown

border

Further

sunburns

to red

irregular,

treatment

to black

color

as direction

variability

by the stage

Source: Data from Lazarus et al. (16), Callen et al. (17), Lebwohl et al. (18), and Maibach and Zhai (19).

Source: Data from Lazarus et al. (16), Callen et al. (17), Lebwohl et al. (18), and Maibach and Zhai (19).

Cocarcinogens or Promoters

These substances accelerate the cancer after it is induced, typically a 4- to 5-ring hydrocarbon or a noncarcinogenic chemical such as sulfur (used as a pesticide in grapes, citrus, and other fruits) (1,41).

Physical Carcinogens

Mechanical trauma causing chronic irritation, heat, and scars from chemical or thermal burns comprises the physical causes of skin cancer (1,41).

Ionizing Radiation

Seen rarely in agriculture, exposure to radiation caused by nuclear accidents, nuclear attacks, or accidental exposure to nuclear materials can lead to dry skin, thickening, hyperkeratosis, ulceration, and cancer (1,41).

Nonionizing Radiation

The sun, with mid-UV rays (290 to 320 nm), is a potent cause of skin cancers and actinic keratoses. Typically BCC is more common than SCC; melanoma rarely presents. Chemical and ultraviolet B (UVB) carcinogenesis have an additive effect (1,41,43).

Prevention

Prevention consists of avoidance of exposure, good hygiene practices, covering of skin surfaces, and sun block on those skin surfaces that can't be covered. However, care must be taken because some sunscreens can increase the penetration of some herbicides (44,45).

Diagnosis

In farming communities, community-based screening programs have been found effective in discovering agricultural skin cancers at an early stage. Newer approaches involving instrument-assisted screening and detection methods are under development (45,46).

Clinical diagnosis of skin cancers is based on the morphology of the lesion, area of skin where it is presenting, history of growth, and biopsy results (24,47).

Management

Surgery is the most popular treatment for BCC and SCC; cryotherapy is the most common for AK. Excision completely removes the skin cancer but can leave unsightly scars. Other techniques for removal include laser removal techniques, carbon dioxide resurfacing of photo-damaged skin, cryotherapy techniques, topical antimetabolites, electrodesiccation, and irradiation. Treatment of melanomas may require a complicated combination of excision, adjunctive immunotherapy or chemotherapy, and irradiation (47,48).

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