Verslag OT2010

Skin tumours: there's more beyond the surface
Saturday 6 and sunday 7 february 2010, Soesterberg.

Simone Thissen, DVM, Venucon

(Soesterberg, THE NETHERLANDS) – For the fifth time the annual Dutch veterinary oncology conference ‘ONCOlogisch Treffen’ took place on February 6-7 2010 in Soesterberg. The theme of the conference was "Skin tumours: there’s more beyond the surface’. A multidisciplinary panel of renowned speakers from across the US and Europe discussed skin tumours in dogs and cats and two specialists in human medicine shared their expertise on mastocytosis, melanoma and the epidemiology of human skin tumours in the Netherlands. Over 120 veterinarians from different European countries visited the two-day congress and enjoyed an inspiring and high-level educational program.

Skin tumours: prevalence, diagnostic procedures, cytology and histology

Dr. Chiara Noli (Dip ECVD, Italy). The incidence of skin tumours in carnivores can vary considerably depending on the region and breed popularity in a country. It varies from 728 cases of cancer in skin and connective tissue/100,000 dogs/year, and 84 cases in the cat in the first studies, to 1,437 per 100,000 dogs/year in a more recent study. Unlike tumours in general, most skin tumours in the dog are benign (57% of mesenchymal tumours, 85% of epithelial tumours). In the cat mesenchymal tumours (47% of all skin tumours) are found to be malignant in 80% of the cases, while epithelial tumours are benign in 60% of cases. The prevalence of various neoplasms, age of affected dogs and sites of occurrence (trunk 30%, head and neck 21%, extremities 19%, (peri)anal area 8% and tail 4%) are more or less similar between surveys in different countries. The odds of tumour malignancy linearly increased with increasing age of the dog by a factor of 1,1 per year. Purebred dogs have a two times higher risk of neoplasm presence than mongrels.

Cytology is a very useful, inexpensive and rapid method of obtaining important information about skin tumours. The animal doesn’t need to be anesthetized, there is no risk for metastases and this method is very sensitive in mast cell tumours and many round cell tumours. Disadvantages are that this examination only provides information on morphology of single cells and not on the histology and invasion of surrounding tissue. Furthermore mesenchymal proliferations may be difficult to interpret. A histological examination is therefore mandatory in all excised skin tumours. Histology is more diagnostic in most cases, shows cell organized in structures, tissues and organs, can usually discriminate well between tumour and inflammations, immunohistochemistry and lymphocyte clonality can be performed as well as infiltrative growth and tumour grading. Pitfalls are the need for general anaesthesia, the higher costs, a minimum of 3 days processing, requirement of an outside lab, and mast cell tumours or amelanotic melanomas may be missed without an experienced dedicated veterinary pathologist. Noli emphasizes the importance of a proper and complete filled out history sheet for the pathologist with information on species, breed, sex, age, description and localization of the lesion(s), time of appearance (growth rate) and don’t hesitate to use special staining to mark margins and positions (anterior, right side etc) and write down special requests.

Surgery and wound closure

As surgery is still the number one best tumour therapy, Michael M. Pavletic, DVM, DACVS, gave an overview of different methods for surgical wound closure. Assessment of the wound condition, size, location, regional skin tension, condition or health of regional skin and other factors affecting wound healing (e.g. very thin skin in grey hounds), will help selecting the right method. Ideally wound management is performed under the same general anaesthetic procedure as the surgery: it is faster, easier and more economical. Large wounds and problematic defects in body regions lacking skin or mucosal apposition form a dilemma. Supplemental closure options for these wounds include:

• second intention healing
• tension relieving techniques
• skin stretchers: to pre-stretch skin prior to elective surgery, close large wounds (especially on trunk) and to reduce wound tension postoperatively
• local flap techniques
• axial pattern flaps
• skin grafting
• tissue expander

The transposition flap is especially effective for a variety of body regions, axial patterns flaps are suitable for large wounds, and skin grafts for lower extremity defects and large trunk wounds. Free skin grafts are not a preferred technique for surgical wounds after tumour resection as the risk for failure is greater compared to application to a stable granulation bed. For a successful flap technique 10% of circulation is needed to keep the flap viable. Each technique has specific advantages and disadvantages and sometimes combining of techniques is the most effective method. Pavletic prefers the use of tissue expanders in lower extremity defects. In his book "Atlas of Small Animal Wound Management and Reconstructive Surgery" (3rd edition 2010), he provides comprehensive information on wound healing, - closure techniques, - management and common wound complications.

Radiation therapy: the second most important cancer treatment

Radiation is the second most important cancer treatment modality after surgery. Barbara Kaser-Hotz, Dipl. ACVR (Radiology and Radiation Oncology), Dipl. ECVDI, Switzerland, explained: "The goal of radiation, as with all cancer treatment options, is to maximally damage the tumour, while minimally destroying normal tissue. In humans 29% of oncology patients is cured by radiation therapy alone although cancer therapy in general is often a multimodality approach using surgery, and medical therapy in combination with radiation. Radiation is used to treat local and regional disease and main indications are tumours of the head and neck (nasal -, brain- en oral tumours), skin and soft tissue tumours (mast cell tumours, squamous cell carcinoma, melanoma etc) and some other tumours (bladder, urethra, osteosarcoma, spinal tumours, thymoma etc) and benign lesions, for example a lick granuloma. Radiation is typically given in several sessions, called fractions, and the fractionation schedule depends on the normal tissue in the radiation field and the tumour type. Brain tissue for example doesn’t tolerate large fractions, carcinomas respond best tot multiple, frequently applied fractions, whereas sarcomas tend to respond best to larger and fewer fractions. In contrast to human medicine where 20-30 fractions are commonly applied, the amount of fractions in veterinary oncology is usually 12-18 or, in palliative protocols, 3 to 5 large fractions, as animals need to be anesthetized. The goal of palliative treatment is to alleviate pain, stabilize and improve quality of life, so side effects should be minimal. Side effects can be acute at the end of therapy, can last for 2-3 weeks and include mucositis and dermatitis. The dermatitis should not be treated with an ointment but the owner can apply cold black or green tea for alleviation. Late side effects can occur months or years after therapy (5% in humans) and include brain and/or spinal cord necrosis and cataract."

Mast cell disease: What’s new?

Barbara Kitchell, DACVIM, USA. Malignant transformation of mast cells is a rare event in humans but a common event in dogs and to a lesser extent cats. Canine cutaneous mast cell tumours (MCTs) occur in older dogs (mean age 9 years) but any age may be affected. There is no sex predisposition but some breeds are predisposed, like flat nosed English breeds (Boxer, Boston terrier, Bullmastiff), Shar Pei’s, Golden - & Labrador retrievers, Cocker spaniels, and Schnauzers. In dogs MCTs are most commonly found on the trunk, accounting for approximately 50% to 60% of all sites. Unlike in the dog, the head and neck are the most common sites for MCTs in the cat followed by the trunk and limbs. Mast cells, normal and neoplastic, contain and release important biologically active substances: heparin, histamine, eosinophilic chemotactic factor and proteolytic enzymes. The pathogenesis of MCTs includes genetic factors, exposure to environmental carcinogens and more recently mutations in the proto-oncogene c-kit, which is the receptor for hematopoietic stem cell factor in canine MCTs. Have been identified by several investigators,, it is estimated that these mutations exist in 38% of canine mast cell cases, and are associated with more aggressive biologic behaviour and higher tumour grade. The role of c-kit mutations in CMT is being actively explored, as receptor tyrosine kinase inhibitors are a class of drugs tailored to inhibit aberrant signalling through pathways such as c-kit.

Therapy for mast cell disease varies depending upon the histologic grade of disease, the clinical stage and the availability of modalities such as radiation therapy.

Surgery is still the mainstay of therapy for local mast cell disease and traditionally a 3 cm margin into normal tissue is recommended. Recently a study suggested that 2 cm lateral margins and a deep margin of 1 fascial plane is sufficient to clear the local disease, especially in Grade I tumours.

Radiation therapy is overall successful for incomplete margins or non-resectable disease with a tumour free rate varying from 79% - 96% at 1 year to 77% - 88% at 2 year. Chemotherapy may be reserved for dogs with non-resectable or metastatic lesions. The efficacy of chemotherapy in preventing recurrence or metastasis of MCT has not been documented. Glucocorticoids are most commonly used in treatment of this disease. Agents that have shown efficacy include vincristine, vinblastine, cyclphosphamide and docorubicin. The nitrosourea agent CCNU has been reported to induce responses in dogs with metastatic mast cell disease. However, the response to any of these agents is unpredictable and typically short lived in disseminated canine mast cell disease. Investigational therapy with toceranib, an inhibitor of receptor tyrosine kinase signalling, especially of c-kit, VEGF-R and PDG-R, has been carried out in the dog, and those dogs with a receptor mutation in c-kit were the ones most likely to respond. The registration trial showed on overall response rate of 42.8% (21 Complete Response, 41 Partial Response) and adverse effects were considered tolerable. However this product is not yet commercially available and has the potential for significant side effects. Other receptor tyrosine kinase inhibitors have been evaluated in the dog, including masitinib (Masivet®), which resulted in improvements in survival and response rates with median time to progression of 253 days for treated vs. 75 for placebo treated dogs. Imatinib mesylate (Gleevec®) has been reported to benefit dogs whether or not the tandem duplication mutation in the activation domain of c-kit is present. However, owners who elect imatinib therapy for their dog should be counselled that lethal idiosyncratic hepatobiliary necrosis has been reported. In a recent study 21 dogs with measurable MCT showed response within 14 days in 10/1 cases, and those dogs with kit mutation in exon 11 had a 100% response rate.

Mast Cells and mastocytosis in humans

Prof. Hanneke Kluin-Nelemans, Groningen, the Netherlands. Mastocytosis is a well-defined but rare disease in people with major and minor criteria. Most patients are referred several times before the diagnosis is made. The large majority of patients suffers from indolent mastocytosis with many symptoms but the disease is not life shortening. The disease is divided in cutaneous mastocytosis and systemic mastocytosis. Cutaneous mastocytosis, that almost always involves urticaria pigmentosa, is the most prevalent form and is seen in children, where it disappears in the vast majority spontaneously when approaching puberty or even earlier. Systemic mastocytosis is uncommon and is caused by an increased number of mast cells in the body. The clinical pattern is dominated by the release of mast cell mediators: histamine, heparin (>> osteoporosis), tryptase, TNF etc. Patients with systemic mastocytosis can have symptoms related to involvement of the hematopoietic system, the GI system, the skin, and the immune system: anaphylactic shock after receiving opioids, contrast fluids, anaesthetics or a bee sting, without being allergic, pruritus, flushing, diarrhoea, abdominal cramps, a fracture after a minor accident, severe osteoporosis, weight loss, night sweats, hepato- en splenomegalie, ascites, thrombocytopenia, leucopenia and anemia. The aggressive form of the disease will usually result in acute myeloid leukaemia or other myeloprolific diseases with the same kit mutations as in malignant mast cells.

The diagnosis is made by showing the presence and increased amount of abnormal mast cells, clusters of more than 15 cells in the bone marrow and with abnormal morphology. Diagnostic steps include a bone marrow biopsy (histology, immunofenotyping and kit analysis (PCR)), a serum tryptase test, osteoporosis screening and a CT scan or ultrasound of the abdomen. It is important to know the exact location of the mutation on the receptor to be able to use specific tyrosine kinase inhibitors.

Therapy is usually symptomatic focussing on histamine release using H1- and H2-antagonists and avoidance of triggers that induce the release of mediators. Therapy includes:

1. Avoidance of triggers that induce the release of mediators: opioids, alcohol, contrast fluid, aspirin, NSAID’s, stress, skin irritation and heat exposure.

2. Histamin antagonists (Nalcrom®)

3. Insect stings monitoring and an epi-pen (when history of sting)

4. Osteoporose monitoring

There is no scientific evidence for dietary intervention. Real eradication therapy including interferon, chemotherapy or TKI is restricted for severe, aggressive cases and mastoleukemia. In these cases the following agents are available:

1. Interferon alfa usually in combination with prednisone

2. Chemotherapy: the majority is not effective in mastocytosis in men, except for cladribine. Side effect: T-cell lymphocytopenia (AIDS- like disease): patients are very susceptible for fungal and viral infections.

3. Tyrosine kinase inhibitors: the future in mastocytosis. Several available. Gleevec® is mostly used with a survival rate over 90% for 5-10 years in people with CML (Chronic Myelogenous Leukemia). Newer products as dasatinib, nilotinib and midostaurin are available. The latter may be important in mastocytosis and a pilot study is being performed worldwide.

Epitheliotrophic lymphoma in the dog

Cutaneous lymphoma is characterized by neoplastic proliferation of lymphocytes in the skin. Two forms are documented: Non-epitheliotrophic lymphoma, that only involves the dermis and can be both B- or T-cell lineage and epitheliotrophic lymphoma that involves the epidermis and/or mucosa and can also include the dermis and/or submucosa with only T-cell involvement. Canine epitheliotrophic cutaneous T-cell lymphoma (CTLC) is the most common form of cutaneous lymphoma in dogs and accounts for approximately 5% of all canine lymphoma subtypes. CTLC consists of three different clinical and histological forms: pagetoid reticulosis, mycosis fungoides (MF) and Sézary syndrome. The disease in dogs resembles the human syndrome, but in 80% of the canine cases, neoplastic cells are CD4(-)/CD8(+) versus CD4(+)/CD8(-) in 90% of the human patients. CTLC is a disease of aged dogs, the median onset being 9 years of age. There is no real breed or sex predisposition. Prognosis is poor with a survival time from a few months to a maximum of 2 years. Treatments frequently have a low efficacy and are challenging for two reasons. First, the pharmacology of the skin requires drugs that reach the lesions at therapeutic levels (high distribution volume and lipophilicity). Secondly, T-lymphocytes and cytotoxic CD8 positive lymphocytes in particular are notoriously hard to kill due to the relative insensitivity to apoptotic signals. Thus, dogs with generalized T cell lymphoma have a lower response rate, duration of remission, and overall survival than dogs that present with B cell lymphomas. In general, the standard rules of cancer therapy apply to these tumours: surgically excision of solitary lesions, with consideration given tot adjunctive chemotherapy. However, most cases present with multiple cutaneous lesions, ruling out surgery as an option. Other therapy options include radiotherapy, phototherapy, topical therapy and systemic therapy with fatty acids supplementation. Linoleic acid (safflower oil) 3 ml/kg twice weekly has been anecdotally associated with cutaneous lymphoma regression,. Systemic chemotherapy may be used in combination with corticosteroids such as prednisone. Lomustine or CCNU is a non-traditional alkylating agent that is used primarily for treatment of brain tumours in human patients because of its high volume of distribution and lipophilicity. Lomustine has been used in dogs with cutaneous lymphoma with an initial pilot study reporting complete remission in all 7 dogs treated. Duration of response ranged from 2 – 15 months. In more recent studies total remission ratios varied from 33% to 26% for a median duration of respectively 86 and 95 days. The main reported toxicity of lomustine chemotherapy is myelosuppression, especially in the form of neutropenia and thrombocytopenia, which can be severe at the higher end of the dose range. Another reported side effect is hepatotoxicity. These results demonstrate activity of lomustine chemotherapy for canine CTCL, but further research is warranted to evaluate combination protocols, standardize an optimal dosage, and evaluate efficacy when used for previously untreated CTCL.

Melanoma

In contrast to people where exposure to UV radiation from the sun on an unadapted white skin forms the most important risk factor for the development of melanomas, in dogs genetic predisposition and chemical carcinogenesis (licking chemicals from coat) play a role. The oral cavity represents the fourth most common site of cancer in dogs and malignant melanoma is the most common canine oral neoplasm, which has a fair to a poor prognosis with only about 25% of patients surviving one year after treatment. Ocular and cutaneous melanomas in the dog are most commonly benign, with the exception of digital melanomas that have a high metastatic rate. In cats, melanoma is uncommon (<1% of all tumours).

Surgical resection with 1-2 cm margins is recommended where feasible. The use of radiation therapy is limited, because melanomas are relatively resistant to radiotherapy and the local therapy won’t address the life-limiting problem of systemic spread. Chemotherapy has been attempted and resulted in a limited number of durable remissions. Melanomas have been found to express Cox-2 in vitro, so adjunctive therapy with Cox-2 inhibitors is worthy of additional investigation.

In human oncology immune and gene therapy is an area if intense investigation but the main focus is on early detection and primary prevention.

In dogs antitumor strategies have been attempted and long-term survival of dogs with advanced malignant melanoma was achieved after DNA vaccination with xenogeneic human tyrosinase antigen (Merial). This vaccine is now commercially available by limited license to veterinary oncologists, and ongoing investigations are being conducted in extended field studies. Gene therapy has also been employed experimentally in dogs with malignant melanoma. Initial evidence suggests that this therapy has some potential utility in dogs with spontaneously arising melanoma, in that dogs were able to develop antigen-specific cytotoxic T-lymphocytes exposure to the vaccine.

Photodynamic therapy: the treatment for cutaneous squamous cell carcinoma

Photodynamic therapy (PDT) has been rarely used in Veterinary Medicine in the past to treat cancer. However, this technique offers an elegant treatment option for small, superficial squamous cell carcinomas (SCC) in cats. Approximately 15% of all skin tumours in cats are SCC. The combination of light, a photoactive drug that is accumulated within the tumour (after injection) and oxygen will lead to a photochemical reaction that will directly destroy the tumour cells, as well as indirect damage via impairment of tumour vasculature. The limitation is the limited light penetration into tissue- therefore only superficial tumours are amenable to PDT. PDT can be repeated without hesitation, as there is no accumulation of toxicity and side effects are rarely seen. The overall response rate initially is 80-100% and PDT can be combined with other treatment options. In humans PDT is also used to treat superficial oral and oesophageal tumours, as well as urethral and bladder tumours.

Basic science and clinical science award

A special moment during the conference was the presentation of a double award by the Dutch Cancer Fund for Animals (NFKD) to Sarah van Rijn and Lona van der Duijen Schouten for their contribution to combating cancer in companion animals. For the first time the NFKD awarded both a Basic Science Award and a Clinical Science Award.

Sarah van Rijn received the Basic Science Award for her thesis ‘Biological aspects of the canine pituitary gland’. Sarah compared canine microadenomas and macroadenomas in their expression of proliferation markers. She concluded that there is no significant difference in proliferation rate between the different pituitary adenomas seen in dogs, but merely a disruption of the regulation of the cell cycle. She also investigated the role of stem cells in pituitary adenomas and her observations undermined the hypothesis that the so-called Side Population (SP) cells mainly consists of undifferentiated stem and progenitor cells. Therefore, further studies are needed to analyse the SP in more detail and to support the presence of the stem/progenitor cell phenotype in the canine pituitary gland.

Lona van Duijn Schouten received the Clinical Science Award for her thesis ‘Lanreotide and cabergoline treatment of dogs with Cushing’s Disease’. Cushing’s Disease in human patients and dogs is mainly caused by an anterior pituitary adenoma. Treatment choices include transsphenoidal selective adenomectomy or treatment with a competitive inhibitor of 3ß-hydroxysteroid dehydrogenase (trilostane). Due to the similarities between dogs and human patients with CD, this study was conducted to see if dogs can be a suitable animal model in vivo for the medical treatment options of CD in human patients. The study focused on the effects of treatment of pituitary dependant hypercortisolism in 9 dogs with lanreotide autogel for 6 months (and 3 months with cabergoline if necessary). The results showed that lanreotide has effects on UCCR, plasma hormones and tumour growth in dogs with CD. This suggests that administration of somatostatin analogues in combination with dopamine agonists will have beneficial effects on humans with CD. However, further research is necessary to support this.

Thanks to this award and the funding provided by the NFKD, Sarah was able to attend and present her findings at the ESVONC (European Society of Veterinary Oncology) spring congress that took place from 18-20 March 2010 in Turin. Furthermore she will be spending a week at a major European veterinary oncology clinic to gain practical experience.