techniques may include local excision, segmental
posthioplasty (‘reefing’), partial phallectomy, and
en bloc penile and preputial resection with penile
retroversion (Scott 1976; Markel et al. 1988; Doles
et al. 2001; Archer and Edwards 2004). Use of CO2
laser for surgical management of MC-SCC resulted in
complete resection without recurrence in 78% of cases
(McCauley et al. 2002), suggesting a viable method for
MC-SCC removal. When MC-SCC metastasis to regional
lymph nodes is detected, those nodes should also be
excised.
Cryotherapy
Cryotherapy has been used successfully in the
management of MC-SCC, often after surgical
debulking (Joyce 1976; Hilbert et al. 1977; Harling et
al. 1983). This involves application of liquid nitrogen
at -196°C (by spray or probe) to lyse tumour cells
through intracellular ice formation. The best results
are often for treatment of early or precancerous
MC-SCC, especially on the penis and prepuce (Bosch
and Klein 2005; Stick 2006).
Hyperthermia
Hyperthermia has been used as an adjunctive therapy
following surgical debulking for equine MC-SCC (Grier
et al. 1980; King et al. 1991; Moore 1992). In one
study, 8 horses with ocular MC-SCC were treated
with hyperthermia, half of which had been treated
previously with surgery, cryotherapy, radiotherapy or
immunotherapy; 75% of these tumours regressed and,
of the 25% that required additional hyperthermia,
66% regressed (Grier et al. 1980).
Radiotherapy
Radiotherapy uses ionising radiation to kill tumour
cells by damaging nucleic acids and protein through
free radical formation. Two forms of radiotherapy
include teletherapy and brachytherapy. Teletherapy
is high energy x-ray or g-ray radiation that is applied
80–100 cm from the tumour by a linear accelerator or
cobalt-60 unit and thus requires multiple treatments
under general anaesthesia. Teletherapy is used for
advanced tumours that cannot be completely excised
and, although it is often used palliatively, it has been
curative for periorbital MC-SCC in ~50% of cases
(Theon 1998).With respect to brachytherapy, success
rates for treatment of periorbital MC-SCC using
iridium-192 were 82% at one year post treatment and
64% at 5 years (Theon and Pascoe 1995). Strontium-90
is b radiation and is directly applied with a probe
to the neoplastic tissue. Because the radiation only
penetrates ~2 mm, strontium-90 should only be used
for superficial lesions. In one study, 83% of limbus,
cornea or third eyelid MC-SCC were successfully
treated with strontium-90 radiation when combined
with superficial keratectomy and permanent bulbar
conjunctival grafts (Plummer et al. 2007). Periorbital
MC-SCC treated with several adjunctive forms of
radiation therapy had a significantly lower recurrence
rate (12%) than those treated without adjunctive
radiation therapy (44%; Mosunic et al. 2004),
supporting its use as an effective treatment modality.
To summarise, brachytherapy is often used as an
adjunctive therapy following surgical debulking of
MC-SCC but may also be used alone for small lesions
that cannot be completely excised. Complications
include loss of hair pigment, permanent epilation,
palpebral fibrosis, and cataract and corneal ulceration
(Theon and Pascoe 1995; Theon 1998). Some cutaneous
tumours suitable for brachytherapy are also good
candidates for intratumoural chemotherapy, and the
choice between the 2 modalities is based on tumour
type, size, degree of invasiveness, predicted cosmetic
and functional outcome, access to a radiation therapy
facility, and cost.
Chemotherapy
Intralesional and topical chemotherapy have
been used with some success for equine MC-SCC.
Intratumoural cisplatin, 5-fluorouracil (5-FU),
mitomycin-C and bleomycin have been used to
treat equine MC-SCC. Cisplatin (cis-diammine
dichloroplatinum) inhibits DNA synthesis by binding
to DNA. Two different approaches allow controlledrelease administration: intralesional injection of a
viscous fluid and implantation of biodegradable
beads. The first method involves reconstitution of
cisplatin powder with sterile water at a concentration
of 10 mg/ml, followed by mixing with sesame seed
oil (60%) and sorbitan monooleate (7%) by use of the
pumping method (Theon et al. 1997). This results in 3.3
mg cisplatin/ml, and the dosage is 1 mg cisplatin/cm3
of tissue. The treatment recommendation includes
4 intratumoural injections given at 2-week intervals
(Theon et al. 2007) and is often initiated immediately
following surgery (Theon et al. 1993, 1999, 2007).
Cisplatin beads are typically implanted through stab
incisions at 1.5 cm intervals in the tumour bed and
surrounding skin. It is recommended that tumours >1.5
cm be debulked prior to implantation, while tumours
<1.5 cm be treated with bead implantation alone
(Hewes and Sullins 2006). Intratumoural cisplatin,
in the injectable or bead formulation, yields similar
success rates for the treatment of MC-SCC (Hewes and
Sullins 2006; Theon et al. 2007). In horses with MC-SCC
that were treated with cisplatin injections, one study
reported a relapse-free rate of 65% (Theon et al.
1993), while a second study reported an 88% success
rate (Theon et al. 2007). Similarly, approximately 85%
of horses with MC-SCC treated with perioperative or
post operative cisplatin injections were tumour-free
after 4 years (Theon et al. 1999).
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