Collectively, it may be concluded from clinical studies evaluating the effectiveness of systemic chemotherapy for treating
mast cell tumors that adjuvant systemic chemotherapy for treating residual microscopic disease is an alternative to curative-intent
radiation therapy. However, additional studies are required to better define the true effect of different systemic chemotherapy
protocols for treating residual neoplastic mast cell disease. Systemic chemotherapy administration is not restricted to referral
centers, so it is a more widely available therapeutic option for both pet owners and veterinary practitioners. If you choose
to treat an animal with adjuvant systemic chemotherapy, you must know the basic precautions required for the safe handling
and administration of chemotherapy.
Intraregional deionized water
Mast cells are sensitive to changes in osmolality and when exposed to hypotonic solutions, will undergo cellular swelling
and ultimately membrane lysis. Based on this cellular response, several studies have evaluated the safety and efficacy of
intraregional deionized water injections as an adjuvant treatment for incompletely resected cutaneous mast cell tumors. Although
all studies suggest that intraregional deionized water injections are well-tolerated, a marked disparity exists among studies
regarding the efficacy of the injections in preventing local tumor recurrence.28-30
In one study, the survival times and tumor recurrence rates were compared between two treatment groups: dogs receiving only
surgical resection (n = 28) and dogs receiving surgical resection and adjuvant intraregional deionized water injections (n
= 27). Disconcertingly, dogs treated with surgery and intraregional deionized water injections experienced greater local tumor
recurrences and shorter overall survival times than did dogs treated with surgery alone.29 These results suggested that intraregional deionized water injections may negatively influence the outcome of dogs with mast
In direct contrast, two other reports discuss intraregional deionized water injections as being effective when used in an
adjuvant setting. In one study, 74 dogs with 118 mast cell tumors were treated with surgery alone or surgery combined with
intraregional deionized water injections.28 The local tumor recurrence rate in dogs receiving only surgery was 52.6% (10/19), while dogs treated with surgery and the
injections had a recurrence rate of 26.2% (26/99). Furthermore, in a recent pilot investigation, only one dog out of 17 with
incompletely resected cutaneous mast cell tumors treated with adjuvant intraregional deionized water injections developed
local tumor regrowth.30 Although intraregional deionized water injections may be reasonable for the adjuvant treatment of small, low- to moderate-grade
mast cell tumors, their use is unlikely to be beneficial in treating diffuse, infiltrative tumors or aggressive grade III
mast cell tumors.
The cost-effectiveness and ease of administering intraregional deionized water injections makes this investigational adjuvant
therapy attractive. However, the direct contradictory results from clinical trials assessing their efficacy for treating resected
cutaneous mast cell tumors remain problematic and a reason for concern. Until further studies are conducted to better clarify
the role of deionized water injections, it remains difficult to wholeheartedly support this adjuvant treatment option. Additionally,
despite being reported as well-tolerated, it is the experience of many clinicians that deionized water injections can cause
moderate pain and discomfort.
Brachytherapy is a radiation treatment modality in which radioactive material sealed in needles, seeds, wires, or catheters
is placed directly into or near a tumor. Treatment with brachytherapy may be intracavitary, intraluminal, or interstitial.
For interstitial brachytherapy, radioactive materials are placed directly through the body tissue encompassing the tumor.
Iridium-192 is a radioisotope capable of releasing both gamma and beta particles and can be used as a radioactive source for
Recently, interstitial brachytherapy with iridium-192 has been evaluated as an adjuvant treatment for cutaneous mast cell
tumors in dogs.31 In this study, nine dogs with microscopic residual disease and two dogs with macroscopic disease were treated with interstitial
brachytherapy. Five of the 11 treated dogs ultimately had local tumor regrowth at a median of 1,391 days. Although a high
percentage of dogs experienced tumor recurrence, the long median latency period before tumor regrowth was impressive. Given
the extended period between initial brachytherapy and local regrowth, it remains a possibility that some of the dogs identified
as treatment failures may actually have been affected with de novo tumor formation.
Interstitial brachytherapy offers some advantages over conventional external beam megavoltage radiation therapy, including
more localized energy deposition, greater normal tissue sparing effect, and decreased total treatment duration. Unfortunately,
the number of facilities offering brachytherapy is limited, and in conjunction with the observed high incidence for local
tumor regrowth (5/11), it is difficult to recommend interstitial brachytherapy as a realistic or practical adjuvant treatment
option for incompletely resected mast cell tumors.