Hello again Dannie!
I'm so glad you have a medical background as that is going to make it much easier for me to explain.
Hemangiopericytomas are a soft tissue sarcoma. I am going to start with giving you a FAQ prepared by a veterinary oncologist FOR veterinarians. This article and the one below are from a website (http://www.vin.com/) that is for veterinarians to discuss medicine with other general practitioners as well as to ask advice from veterinary specialists such as oncologists and surgeons.
Soft Tissue Sarcomas Medical FAQs
What tumors are we talking about here?
The three most common soft-tissue sarcomas (STS) are fibrosarcoma, hemangiopericytoma, and peripheral nerve sheath tumor. Less common STS include schwannoma, leiomyosarcoma, 'spindle cell tumor' (unspecified), neurofibrosarcoma, liposarcoma, and myxosarcomas. Hemangiosarcomas, rhabdomyosarcomas, and lymphangiosarcomas are also STS strictly speaking, but since they behave differently from other more typical STS, they are not covered in this FAQ.
What is the best way to approach surgery of soft-tissue sarcomas (STS)?
Soft-tissue sarcomas (STS) often extend well beyond the visible mass, much like mast cell tumors. For this reason you should ALWAYS know when you are going to excise a STS - ie diagnose before excision. This can be done by performing a fine needle aspirate (FNA) and cytology on every mass before it is excised. FNA can often be easily examined in-house, although the practitioner's level of training, interest and experience in cytological diagnostic interpretation will strongly impact the likelihood of a correct diagnosis. If a clinician lacks experience, interest or appropriate staining techniques, or has any hesitation in the cytological diagnosis, the sample should be sent out for specialist interpretation. Many STS are difficult to differentiate from fibroplasia (a benign process), requiring specialist interpretation. Additionally, Diff-quik staining is inferior to Giemsa staining, and may also hamper accurate in-house diagnosis. Thus, clinicians are advised to make 2 sets of smears - one for in-house examination (if desired), and a second (unstained) for submission to a diagnostic pathology service.
Once a STS is confirmed, the tumor is excised with 3cm lateral margins, 1 fascial layer deep. This avoids going anywhere near the tumor during your surgery and thereby adheres to an important principle of cancer surgery - en bloc resection. Some oncologists prefer to perform an incisional biopsy and histopathology to obtain a histological grade prior to performing the excisional biopsy, for prognostic purposes and therapeutic planning.
However, clinicians should be aware the up to 40% of STS that have "clean margins" histologically, may recur ("clean but close" margins are obviously at higher risk for such local recurrence). It is important to notice that we will often recommend advanced imaging (CT or MRI) prior to excision of a STS, especially when the mass is large, firmly attached to the underlying tissue, and/or in a location where wide margins may be more difficult. Consulting with a boarded surgeon is also recommended in such situations. This also applies to ALL feline vaccine site sarcomas.
The pathologist has said that a tumor I excised is a STS and margins were dirty. What should I do?
STS (including hemangiopericytomas, schwannomas, nerve sheath tumors, fibrosarcomas, spindle cell tumors, leiomyosarcomas, but not hemangiosarcomas or lymphangiosarcomas) all tend to have several features in common:
1. They invade well past their visible or palpable margins ("tendrils").
2. They appear to be encapsulated but are not. The pseudocapsule comprises a layer of compacted but actively growing neoplastic cells. This is important because dissecting these out ("shelling") will result in local recurrence.
3. They are locally invasive but late to metastasize. If you effect local control, then you often have obtained a cure.
Thus, if surgical margins were dirty, the treatments of choice are to re-excise en-toto with wider margins all around the original tumor site and/or perform radiation therapy.
To treat these you need to
1. Perform a wide and deep resection. 3cm wide, 1 fascial plane deep. If you cannot do this because of tumor location then get an incisional biopsy and discuss your options with a surgical or radiation oncologist. In some cases, grafts or patches may be necessary to reconstruct the wound site.
2. Stay well away from the edge of the tumor at all times.
3. If necessary, perform radiation therapy to sterilize residual disease if margins were not clean.
What about if the margins are clean or "clean but close"?
If margins are clean, radiation therapy can be considered (see below). This is probably even more valuable if the margins are "clean but close" (high risk of local recurrence). Alternatively, careful monitoring of the site for recurrence, with re-excision can be employed.
Does chemotherapy help with treating STS?
Soft tissue sarcomas are not very chemoresponsive in general and best treated surgically with or without adjunct radiotherapy. Most studies show modest response rates in the range of 20 to 30%. There may be limited rationale for using chemotherapy in STS that appear highly malignant, or have high metastatic potential. It should generally be coupled with surgery and radiotherapy.
Other agents, such as the non-specific immunomodulator Acemannan, have not been critically evaluated, and are not recommended currently.
Does radiotherapy help with treating STS?
There is evidence that adjunct radiotherapy offers a prolonged disease-free interval and survival when used to treat microscopic disease following surgical resection. Several studies have documented long remission and survival periods (>1500 days median survival) in that setting, when postoperative radiotherapy is used. Additionally, it has shown benefit in limb-sparing tumor treatment, with 75% disease free at 5 years in one study. However, as a sole treatment, responses seem poorer than if combined with surgery. Oral STS appear to be associated with poorer prognosis.
Radiotherapy can also be used palliatively in non-resectable STS to offer pain relief, in addition to traditional analgesic therapy.
So, as you can see from this article, STS's commonly are locally invasive, so it is not uncommon to have "dirty" margins with tumour cells extending past the margins and into the tissues. Ideally, treatment would be to surgicallly remove this tumour, as much as possible given the location. As you can see from the article, this means 3cm in EVERY direction. In this location it might be impossible, and I think that is what your vet wants to talk to the specialist about. In terms of radiation therapy, I will quote here from a 2003 conference proceedings.
Clinical Radiation Therapy Western Veterinary Conference 2003 Karelle A. Meleo, DVM, ACVIM, ACVR
Veterinary Oncology Services
Edmonds, Washington, USA
Reviewing the types of radiation available.
Identifying the tumors most commonly treated in veterinary radiation oncology.
Discussing treatment of radiation toxicity.
Overview of radiation therapy protocols.
Either a Cobalt source or a Linear Accelerator is used for megavoltage therapy.
When a patient is treated with definitive radiation therapy, multiple fractions are needed.
Radiation is a localized treatment.
Combining radiation and surgery is often recommended.
The skin and mucous membranes are common areas of acute toxicity.
The eyes, lungs, kidneys, and the nervous system are of concern for toxicity.
Types of Radiation Therapy
Most institutions have either Cobalt or a Linear accelerator (Linac) available. These both produce megavoltage radiation.
Orthovoltage generally does not penetrate as deeply as megavoltage so does limit the types of patients that can be treated.
Some (but not all) Linacs can generate electrons. Electrons are particularly useful in treating superficial areas with sensitive structures (such as lung) underneath.
Definitive vs Palliation Radiation Therapy
We should consider definitive (given with the intent of long term control) therapy in patients:
1. With tumors of low metastatic rate or in tumor types in which the mets can reasonably be controlled with chemotherapy or;
2. For whom the above is true and surgery is not an option either due to the location of the tumor, or due to the owner's reluctance to consider aggressive surgery or;
3. In whom surgery has been performed and there are still neoplastic cells remaining at the surgical margin (especially if #1 above is true as well).
We can consider palliative (given with the intent of managing pain, improving function, and/or maintaining the quality of life) therapy in patients:
1. With tumors of high metastatic rate or known metastases and/or
2. In whom pain management is needed (such as bone tumors).
Tumors Commonly Treated with Radiation Therapy
Advances in surgical techniques such as maxillectomy and mandibulectomy offer many patients excellent long-term control for many of these tumor types. Radiation therapy can be offered as an alternative to surgery or as an adjunct to surgery for many of these patients.
Epulides: Biopsies of these lesions may be acanthomatous epulis, fibromatous epulis, ameloblastoma, or odontogenic tumor.When treated with radiation therapy, 85% are free of disease at 1 year and 67% disease free at 2 years.
Canine oral fibrosarcoma & squamous cell carcinoma: For both of these tumor types, soft tissue resection alone is usually inadequate, especially if the tumor abuts the bone. The reported median survival time for dogs with oral sarcomas treated with surgery and radiation therapy is 540 days.
Tonsillar squamous cell carcinoma (SCC) is a very aggressive disease and is resistant to therapy.
When using radiation therapy alone to treat dogs with SCC of other locations, survival times from 14-17 months have been reported. Younger dogs and those with smaller and more rostrally located tumors have a better prognosis.
Canine Oral Melanoma: Melanomas are considered "relatively" radioresistant. This means we must give a larger radiation dose per fraction than is traditionally used for other tumors. These large dose per fraction protocols usually limits the total dose that can safely be used. This results in fewer fractions (3-6 vs 14-21 normal protocols), being delivered. In one study, dogs given 3 fractions had a median survival time of 7.9 months. In a study where dogs were given 6 fractions of along with Cisplatin chemotherapy, the median survival time was reported to be approximately 12 months. Unfortunately, most patients still succumb to metastatic disease.
The median survival time of dogs treated with megavoltage radiation is 12.8 months with a mean of 20.7 months. In some studies, dogs with sarcomas have been reported to have an improved survival time over dogs with carcinomas. This occurs even though sarcomas are not as radiation responsive as carcinomas. The slow growth rate of sarcomas compared to carcinomas likely explains this difference. It is not necessary to perform rhinotomy to reduce the tumor size prior to radiation therapy.
The survival time for cats treated with megavoltage radiation is similar to that seen in dogs. 44.3% of cats treated are alive at 1 year after therapy and 16.6% are alive 2 years after treatment.
Nasal lymphoma is a notable exception. When radiation is combined with aggressive chemotherapy over 75% of cats are alive at 2 years. Cats treated with 3 radiation treatments did just as well as cats treated with 18 treatments.
In general, megavoltage is recommended over orthovoltage therapy, but many patients treated with orthovoltage have benefited from treatment. Survival times reported in the literature range from 150-412 days. Radiation may be used alone or combined with surgery. Dogs with meningioma have a better prognosis than dogs with glioma. Severe neurologic signs and/or multiple tumors are considered negative prognostic factors.
There are few studies on cats with brain tumors treated with radiation therapy. Surgery alone results in survival times of months to years in cats with meningioma.
Mast Cell Tumors
When treated with surgery alone, 50% of dogs with grade II mast cell tumors will have recurrence or metastasis within 1 year. As 50-60% of canine mast cell tumors occur on the limbs it is difficult to get a complete (2 cm or larger) resection on many of these lesions.
Radiation is indicated in dogs with grade II mast cell tumor who have incomplete resection and who have no metastatic disease. Studies have shown that 86-95% of dogs who are treated post operatively are free of cancer for at least 3 years after treatment.
Radiation is a local treatment and does not address metastatic disease.
Soft Tissue Sarcomas
Among other tumor types, soft tissue sarcomas include: Fibrosarcoma, Hemangiopericytoma, Nerve Sheath Tumor, Leiomyosarcoma, Liposarcoma, Hemangiosarcoma, Synovial Cell Sarcoma, Malignant Fibrous Histiocytoma, and Undifferentiated Sarcoma. With the notable exceptions of hemangiosarcoma and high-grade synovial cell sarcoma, these are characterized by a high rate of local recurrence but a low to moderately low rate of metastasis. Grade is important to prognosis.
In a study of dogs with soft tissue sarcomas treated with radiation following gross resection, 75% were still free of disease 5 years following surgery.
In some cases, it may be beneficial to use radiation prior to surgery. This is frequently true of vaccine-associated sarcomas in cats. It may be safer to treat a smaller field prior to performing surgery than a larger one postoperatively. Radiation will effectively treat the cells that are on the margins of the tumor as they are well oxygenated and often dividing rapidly. Surgery is then performed a few weeks after radiation to remove as much of the radiated field as possible.
Pre operative radiation is not recommended to make a tumor that is grossly unresectable resectable, but can be used to increase the probability that a grossly complete excision will also be microscopically complete. It also helps prevent seeding of tumor cells along the surgery site.
Radiation therapy can be used to temporarily reduce the size of a tumor and stop or slow its growth. This can be helpful in improving a patient's quality of life by relieving pain (especially bone pain), decreasing bleeding, and/or relieving swelling or obstruction. One commonly treated tumor is canine osteosarcoma. Approximately 75% of dogs treated have improved limb function for a few to several months. Because lymphocytes are very radiation sensitive, palliative radiation can play a role for lymphoma patients as well.
For additional information on the use of radiation therapy to treat mast cell tumors and head and neck cancer, the reader is referred to proceeding notes on these subjects.
The skin and mucous membranes are commonly affected during and immediately after therapy. Moist desquamation of the skin, similar to a "hot spot", is quite common. In areas that move or bear weight (such as the stifle or the carpus), lameness may result.
Skin reactions usually are treated with topical antibiotics and analgesics. In the early stages, vitamin E oil and Aloe Vera gel seem to reduce discomfort. When the majority of the field is involved, Silvadene® cream or similar can be applied B-TID. Preventing self-trauma is important, but bandaging should be used only if necessary. Oral antibiotics are rarely needed but can be used. Non-steroidal anti inflammatories can be used for pain, and the author often uses anti inflammatory doses of prednisone if there is lameness or a decreased appetite.
Mucositis is generally managed with anti inflammatory medications and soft food.
Depending on the radiation protocol, acute reactions should be well on their way to healing 10-14 days after the radiation is over. Although a lesion may still be visible, pain medication can usually be discontinued at that point. If the animal is still uncomfortable 3 weeks after radiation is over, consultation with a radiation oncologist is recommended.
KCS and conjunctivitis are common when the eye is in the radiation field. Both can be managed symptomatically. KCS may be temporary or permanent.
Acute pneumonitis may be seen if large volumes of lung are in the field.
Acute nephritis may occur soon after a kidney is irradiated.
The most common chronic toxicities we see are cosmetic. Alopecia, mild skin fibrosis, and a change of coat color are common.
The organ system that is responsible for most chronic toxicity is the vascular system. The vascular endothelium thickens after radiation, leading to narrowing of the vessel and increasing the risk of thrombosis and subsequent necrosis. The spinal cord is especially sensitive to this due to the lack of collateral circulation.
Anti-inflammatory levels of corticosteroids during and for several months following therapy reduce the probability of serious toxicity as they decrease the inflammation within the walls of the blood vessels.
Cataract formation 1 year or longer after radiation is expected when the eye is in the radiation field.
Fibrosis of the lungs is expected if this area is irradiated, however if the volume treated is low, this is not a clinical problem.
Radiation therapy can be used to prolong disease-free time in many common tumors. Treating soft tissue sarcomas and mast cell tumors with a combination of surgery and radiation can be very successful.
If your histology report says, "Tumor cells (may) extend to the excised margin" the best chance of preventing recurrence is immediately post op!
Palliative radiation therapy can be used to improve quality of life.
Acute toxicity is generally short lived and easily managed. Chronic toxicity is rarely serious if careful treatment planning is used
Karelle A. Meleo, DVM, ACVIM, ACVR
Specialty Practitioner, Oncology
Veterinary Oncology Services
So, as you can see from this article, radiation can be very useful, though it is still recommended to remove as much of the tumour as possible.
This all said, it is very encouraging that this tumour was a Grade Two (on a scale of 1 to 4). This means that it is not very aggressive yet, and the cells are only moderately different from normal cells. STS's are locally invasive but slow to metastasize (spread to other parts of the body). So, given that this is a Grade 2 STS, that is suggestive that this might not be a problem to your girl in the near future in terms of spreading. The concerns would be whether the tendrils would grow through the surrounding blood vessels and nerves, which migh result in sudden bleeding.
In summary, this tumour is likely to be slow growing locally and late to metastasize. It probably can not be completely removed so it is likely to recur. Surgery to remove all or part of the tumour might protect the delicate structures near it.. Alternatively, radiation would be helpful to slow down the recurrence of this tumour. Generally, radiation is given multiple times (in multiple "fractions" or treatments) over a short period of time. For example, your dog might need 15 fractions of radiation over 2 or 3 weeks. Each treatment requires an anesthetic. Thus it is likely your girl would be hospitalized at a specialty centre for this procedure.
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