DERMATOLOGY
agents in different concentrations . They accumulate in certain tumours and when subjected to high-fluence ( 200-300 W / cm2 ) light of a specific frequency , keyed to the particular molecule being used , the molecules aggregate into unstable complexes that then restabilise by release of various oxygen radicals which cause lipid membrane , protein and DNA damage . Overtreatment causes regional vasoconstriction and side effects , without increase in toxicity ; undertreatment achieves little , but aggravates the inflammation . This treatment is effective only in lesions < 5mm thick . Treatment is once a monthly , for 1 – 3 treatments , depending on severity and extent . Pre-cancerous actinic keratosis can also be successfully managed using this technique .
Immunotherapy using Imiquimod ( Aldara ; 3M ), animidazoquinolinamine , is an immune system modulator and possesses both potent antiviral and antitumor activity in animal models and humans . Current theories suggest that imiquimod acts both directly by inducing apoptosis and by inducing secretion of pro-inflammatory cytokines . Imiquimod activates macrophages and other cells via binding to cell surface receptors , such as Toll receptor 7 , and thereby induces secretion of pro-inflammatory cytokines such as interferon-a ( IFN-a ), tumour necrosis factor-a ( TNF-a ), and interleukin-12 ( IL- 12 ). These cytokines bias towards a Th1-dominant immune response , which in general is associated with inflammation and tissue injury through activated inflammatory leukocytes and with cytolytic activity through CD8 + -lymphocytes ( Abbas et al 1996 ). Imiquimod can also induce apoptosis directly in a Bcl- 2-family-dependent manner by downregulating antiapoptotic genes such as hurpin and HAX-1 .
Treatment is applied to lesions Monday to Friday , once daily , for 6 – 12 weeks ; inflammation caused by the treatment can occasionally be severe and require NSAIDs .
I reserve this for small / early / superficial lesions in cats due to the cost of the cream . Clients must wear gloves to protect themselves . Efficacy is reported as about 75 %, with a median survival time of 1189 days , although recurrent lesions do seem to respond to the therapy .
5-Fluorouracil use in animals : this drug is rapidly and fatally neurotoxic in cats even as eye drops . In dogs , the tolerance is also very low and if licked it can trigger fatal mucosal sloughing . Don ’ t use in veterinary practice .
CRYOTHERAPY is outdated , painful , disfiguring and has a lower success rate than other therapies mentioned . Do not use this . Poor technique is a major reason for treatment failure ; it requires training and experience and is potentially hazardous to the operator .
RADIATION THERAPY : the use of a linear accelerator to deliver high-voltage ( 4 – 20 MeV ) electrons or photons for the treatment of surface tumours is called teletherapy . This technique has the potential for extreme harm if improperly performed , and all such cases are specialist cases and must be referred to a person with the relevant training . There ’ s a reason it ’ s an entire field of speciality in itself in the US and Europe . It requires a knowledge of radiation physics , radiation biology and management of radiation side effects that cannot be gleaned from a few lectures .
The role of surgery in managing skin tumours . Surgery is an important part of management of these conditions . For some tumours e . g . BCC , HA / HSA , MCT , a properly-performed excision can be curative . In others , e . g . SCC , the surrounding skin is often also on an “ anaplastic march ” that is unstoppable by surgery alone . Surgery then helps debulk larger masses that would not respond as well to wider-field but lower-intensity therapies e . g . imiquimod , PDT , RT . The timing and planning is critical . Discuss this with a specialist BEFORE radiation or PDT PLEASE ! Post-surgical fibrosis decreases the efficacy of other modalities ! ( fig 5 )
Figure 3 . SCC ear pinna removal – This is the degree of surgery required for more advanced SCC of the pinna , and is to be avoided if possible , by appropriate education of the client at first vaccination of the kitten . This sort of cat may be allowed out at night , but not during the daytime .
Figure 4 . PDT – Patient undergoing photodynamic therapy at Inanda Vets . vet360
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