Page 36 - Noninvasive Diagnostic Techniques for the Detection of Skin Cancers

Description of Technique
Topical application of ALA has been shown to produce increased concentration of
endogenous protoporphyrin IX (PpIX), which has high fluorescent yield. 109 Studies have shown
that PpIX accumulates in skin tumors at a much higher concentration than in normal skin. 103,110

Theoretical Advantages
To enhance differentiation between normal skin and tumor, shorter exposure times to ALA
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have been shown to be promising. Newer lipophilic derivatives of ALA have been shown to
increase local bioavailability of these agents and may extend the clinical application of PDD. 112
PDD may be helpful in guiding biopsies, especially in anatomically difficult sites (e.g., nose,
ear), 111 and aid in preoperative planning, although the evidence for this claim is mixed. 113-116
PDD also may be useful in detecting recurrences or multifocal disease. 117 Application of ALA or
other prodrugs has been shown to be especially useful in detecting BCC and SCC.

Theoretical Disadvantages
The use of PDD in melanoma detection has been less promising than in the
nonmelanomatous lesions, because it may not have sufficient good sensitivity and specificity in
detecting the disease, when compared to biopsy. Chwirot 1998, reporting on 90 known
melanomatous lesions, detected only an 82.5 percent sensitivity and a 78.6 percent specificity
using autofluorescence. 118 In a 2008 review, Allison and Sibata conclude that the application of
PDD to melanoma is still “a work in progress.” 119 Recent techniques using laser-induced melanin
fluorescence have been shown to differentiate malignant melanoma from benign lesions. 120
Ultraviolet photography, described below, also relies on the fluorescent properties of melanin.

Variations of Technique
• Ultraviolet light photography. Ultraviolet light is absorbed by melanin. The theory behind
this experimental technique is that illumination by ultraviolet light could reveal irregular
pigment distribution, and therefore could be useful in defining the borders of melanoma
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(e.g., lentigo maligna melanoma). It is unclear how widespread the use of this technique
is in the dermatology community, as we did not identify any other abstracts related to this
technique as used in the detection of melanoma.
• Polarized light photography. This method relies on the fact that reflected light has two
components—one regular reflectance to reflect the skin surface morphology, the other
“back-scattered” from within the tissue. 121 It is useful in the assessment of skin surface
morphology when the proper polarizing filters and techniques are used. It can be used in
the assessment of dermal melanosis. It is not widely used for assessing skin pigmentation;
Taylor 2006 and others have highlighted the limitations of polarized light photography in
darker skinned persons with Fitzpatrick skin types IV, V, and VI. 22,121
• Other topical therapies, principally used in the treatment of nonmelanomatous skin
cancer, such as imiquimod and 5-FU could be used in combination with photography to
highlight skin cancers.

FDA Status
No information was found on the FDA clearance status for the devices of this type on the
FDA CDRH database for use in the diagnostic evaluation of skin lesions.

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