DOSE OF CANCER SURGERY FOR MAST and soft tissue SARCOMA

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DOSE OF CANCER SURGERY FOR MAST and soft tissue SARCOMA

Postby guest » Fri Oct 03, 2003 7:26 pm

PLANNING THE DOSE OF CANCER SURGERY FOR MAST CELL TUMORS AND SOFT TISSUE SARCOMAS

David Szentimrey, DVM, MSc, Diplomate ACVS, Western Veterinary Specialist Centre, Calgary, Alberta, Canada
ACVS Symposium Equine and Small Animal Proceedings 
October 1, 2001


PLANNING THE DOSE OF CANCER SURGERY FOR MAST CELL TUMORS AND SOFT TISSUE SARCOMAS

David Szentimrey, DVM, MSc, Diplomate ACVS, Western Veterinary Specialist Centre, Calgary, Alberta, Canada



2001 ACVS Veterinary Symposium Small Animal Proceedings

 

Keywords: Cancer, surgery, mast cell tumor, soft tissue sarcoma, treatment, dog, small animal

 

Of all the treatment modalities currently available, surgery still cures the greatest proportion of our patients.  This is the front line treatment option in the vast number of patients arriving in your practice.  Most veterinarians are comfortable with surgery and this is where they are able to have the greatest impact to enhance their patient’s life.  Surgery must be administered in a carefully <I style="mso-bidi-font-style: normal">calculated dose that must be customized for each patient.  Surgery is available in “doses” just as antibiotics or prednisone are.  You, the surgeon, determine the dose to administer — low doses, high doses or any increment in between.  The appropriate dose of surgery has a huge impact on your patient.  Achieving clean margins in the elimination of cancer is the single most important factor in determining recurrence and survival. 

 

Achieving clean margins is critical and is in fact, the sole objective in most cases of surgical oncology.  Debulking surgery is the only exception and is usually reserved for palliative surgery only.  <I style="mso-bidi-font-style: normal">Do not sweep the clean margins issue under the rug!  Your clients will be the first to see the cancer grow back if you ignore this critical aspect of cancer surgery!  In many cases clean margins are the single most important factor affecting local recurrence and patient survival.  Whether or not you achieve clean margins is the factor that you, the surgeon, has direct and definitive control over! Plan ahead and succeed.  Even the most experienced oncologic surgeons use cadavers to practice the planned surgery.  This exercise discovers pitfalls in the proposed plan before the surgery commences and is strongly encouraged. 

 

Many veterinary surgeons are frustrated by persistent masses that recur and recur after what appear to be aggressive surgeries.  Clean margins were obviously not achieved.  Owners become frustrated and expenses escalate.  If sound oncologic principles are utilized from the start, expensive repeat procedures can be avoided.  Remember that the first surgical attempt at mass removal carries the best chance for a cure.  Subsequent surgeries are less likely to be successful in removing all cancer.  Second surgeries are complicated by scarred regions, areas of inflammation and cancer that was further disseminated by incomplete previous resections. 

 

To the uninitiated, oncologic surgery is perceived to be overly aggressive.  Surgeons that are consistently successful in achieving clean margins are <I style="mso-bidi-font-style: normal">appropriately aggressive.  They have philosophically split the procedure into two halves.  The first half concentrates on cancer removal at almost all cost.  The second phase concentrates on rebuilding the defect: actually the more daunting of the two tasks.  Most veterinary patients could be rendered free of cancer if the surgeon was not philosophically shackled by tissue closure concerns.  Unfortunately margins are often dictated by tissue closure concerns not cancer resection.  Resist the temptation to fall into this trap.

 

The human surgery experience often incorporates two surgery teams.  The first is the resection team.  The second is the rebuilding/reconstruction team.  The “report card” of the first team is the pathologist’s report of dirty or clean margins (obviously very important!).  The report card of the second team is wound healing and cosmesis.  Complications of wound healing are important but usually not life threatening.  Dirty margins, however, can be life threatening The objectives of the two teams are obviously different and they will achieve their goals more often when they are detached.  In veterinary medicine we do not have the luxury of two surgical teams so we must philosophically divide the two phases of the surgery to achieve the independent goals.  We are often faced with reconstruction dilemmas as the greatest challenge in cancer surgery.

 

Cancer Surgery Inherently Produces the Following Struggle in the Surgeon’s Mind …

Assume I gave you 10 dogs with cancer and your task was to remove all the cancer surgically (assume no metastatic disease).  You were asked <I style="mso-bidi-font-style: normal">not to worry at all about closing the wounds.  I then asked your partner to close all the wounds and not worry at all about cancer, just an open wound to close in front of them.  They would probably get most of the wounds closed.  Do you think you would get clean margins in all 10 cases?   Probably!  The point is that we don’t get aggressive enough because we worry about closing the wound.  Mother Nature usually does not make lots of extra tissue to close big wounds; it is too biologically expensive.  So we compromise the life shorting procedure (getting all the cancer out) in favor of closing a wound.  This circumstance may be due to the fact that the owner sees the incision and makes judgments on your work based on that.  The most successful oncologic surgeons are well equipped with reconstruction options to close the big defects created.  This means skin grafts, flaps, and local and regional flaps.  The real challenge in cancer surgery is reconstruction surgery not really cancer removal.  Cancer removal is the relatively easy half of the procedure.  You will help your patients most by becoming comfortable with a range of reconstruction techniques.  Many references and reconstruction texts/atlases are now available.  The best preoperative advice is to use cadavers and practice the procedure and reconstruction technique you plan to use. 

 

<I style="mso-bidi-font-style: normal">Never peel out or shell out a tumor! This approach guarantees dirty margins.  Shelling out a tumor is easy, immediately surgically gratifying, but leaves peripheral microscopic tumor cells in almost all cases.  The peripheral cells are the aggressive cells of the mass as they are the ones invading and multiplying at the edges.  Removal of the larger, visible central mass merely removes the necrotic tissue bulk that is largely quiescent and often necrotic.  Removal of the central bulk of the mass also gives the remaining cells at the perimeter sole access to local blood supply.  There is a cleavage line of weak tissue between the larger central mass that is shelled out and the peripheral microscopic cancer cells.  This cleavage line or zone is the <I style="mso-bidi-font-style: normal">pseudocapsule and is comprised of a bi-layer of compressed cells: tumor cells centrally and normal cells peripherally.  This cleavage line is invariably the zone where the bulk of the central mass detaches from the patient in shell outs.  Every time a mass is repeatedly shelled out there is a selection process for leaving the aggressive tumor cells of the mass at the invading perimeter.  This is why these tumors grow back faster and faster each time they are removed.  We have probably all witnessed this fundamental cancer experiment in practice.  Save shelling out for lipomas only.

 

Many textbooks suggest a magical 3 cm of margins around mast cell tumors and soft tissue sarcomas … so how can we get 3 cm margins around these tumors?  Realistically, in most cases we can’t specifically accomplish this goal without an amputation or very radical surgery.  So how do we achieve an equivalent of 3 centimeters of margin? This goal may be accomplished by accessing available tissues in the region of the cancer.  We must be creative and think <I style="mso-bidi-font-style: normal">outside of the box of “just cut out and sew up.”  To help clarify this issue, think about how sarcomas invade tissues locally.  These tumors expand beyond the borders of their parent tissue and slowly invade adjacent normal structures.  If the tumor is located within a muscle belly then the expanding tumor is within an enclosed compartment of the muscle fascia.  Muscles are encircled by a fibrous connective tissue sheath.  Tumors are usually very advanced before they penetrate a fibrous sheath or layers of fascia.  When treating cancer early, this fascia can be considered a barrier to tumor invasion in most cases and if removed the deep surface may be considered as the deep border or margin.  In our muscle example, margins may be easily achieved by removing the entire muscle and adjoining tendons.  Most muscles have synergistic brothers and sisters that replace and maintain function.  Unfortunately/fortunately muscle tumors are rare and we can only infrequently capitalize on containment of a tumor within a muscle compartment.  Other fascia for the surgeon to take advantage of includes:  body wall (external abdominal oblique fascia), peritoneum,  antebrachial fascia (elbow to carpus),  epaxial fascia over the back, temporalis fascia over the skull, and any fascia over superficial muscles.  Be creative and remove this usually dispensable fascia and muscle as necessary to get clean margins! Very little morbidity will likely result through fascia removal.

 

Sarcomas are lazy to some degree and will expand in areas of little tissue resistance.  They often initially present as a subcutaneous mass in the loose fatty areolar connective tissue of the subcutaneous space.  Most sarcomas feel like they are subcutaneous in location.  This is true; however, they are often attached to deeper structures by tendrils of tumor and neo-vascular pedicles.  These deeper structures are often the tissue from which the primary cancer originates.  Therefore to truly rid the patient of all cancer (the objective of most surgeries) we must remove all the deep attachments and tissue of origin.  The grade of the cancer will tell us how much safety margin (cuff of normal tissue) to harvest in continuity with the cancer.  High-grade tumors deserve a larger cuff of normal tissue; conversely, low-grade tumors allow a smaller depth of normal tissue while still achieving clean margins.  Sarcomas do grow along fascial planes for a time before penetrating the fascia.  This is the path of least resistance.  Also consider that tumors will grow in this loose areolar space and may have “long roots.”  Consider the tumor biologically as you perform the surgery.  This underscores the necessity of the preoperative histologic diagnosis in planning the appropriate surgical dose. 

 

In many anatomical locations there is deep fascia that will delay the penetration of a sarcoma to deeper tissue compartments.  This fascia can be used as a natural boundary so that an actual 3 centimeters of margin is not essential.  Sometimes an MRI, CT scan or ultrasound may be needed to determine if the fascia is in fact penetrated by the cancer or not.  Often these tests are not practical for some owners and the surgeon must use surgical judgment.  If the fascia is penetrated by the tumor the surgeon must consider this observation in surgery (or on the MRI) and revise the surgical plan to remove all cancer. 

 

Various Anatomic Regions of the Canine Body with Respect to Complete Cancer Resection and Reconstruction.

<I style="mso-bidi-font-style: normal">Antebrachium:  The soft tissues of the canine foreleg are comprised of a series of extensors, flexors and remote control tendons that are enshrouded by tough antebrachial fascia.  This fascia is a natural barrier to cancer disease that originates in more superficial locations (clinically most often the case for mast cell tumors and soft tissue sarcomas).  The fascia starts at the elbow and ends just below the carpus.  Thankfully most mast cell tumors and soft tissue sarcomas on the foreleg are superficial to the fascia.  Obviously, it is not possible to achieve 3-centimeter deep margins on the foreleg of a dog.  If the cancer is above this fascia the deep margin may be the deep surface of the fascia.  Therefore get underneath it several centimeters peripheral to the mass.  Functional impairment is minimal/negligible when large areas of this fascia are removed.  Skin grafting can easily and successfully be performed on the exposed muscles and tendons.  Sometimes the wound is left open to granulate prior to grafting.  Under the fascia there are a large number of exposed tendons that may not support a skin graft.  Allowing granulation tissue to form before grafting may increase graft success.  I find skin grafting the best option for reconstruction of cancer resection beds on the foreleg.  Skin grafts are easily performed, highly successful, and release you from the anxiety of tissue closure concerns.  Skin grafting techniques are detailed in most current surgery texts.  The freedom of knowing you can successfully skin graft will allow you to achieve clean margins in a greater percentage of your cases.  I strongly encourage you to learn skin grafting techniques.  Their use allows you much flexibility in cancer surgery, and they are very easy to perform.  The use of the free skin graft is the single most important tool allowing us to get clean margins on the extremities.  We can remove extensive normal tissue margins and cancer in knowing we have unlimited tissue to close the created defect.  Learn to perform skin grafts … they are your friend!

 

Trunk pedicle flaps may be produced for distal limb defects by supporting the limb to the trunk and fabricating a bi-pedicled pouch that closes the defect.  The pouch is cut down about two weeks later after which time the recipient bed has partially vascularized the pouch.  I find these techniques cumbersome and prefer the use of free skin grafts in most cases.

 

There is functional duplication of many of the muscles on the foreleg so consider selective removal of a muscle(s) if the location of the cancer dictates.  Carpal arthrodesis is very well tolerated in dogs and this gives us more flexibility in removing entire muscle compartments.  Don’t forget about the option of amputation if the local dose of surgery is too high to justify the end result.  This may be especially true in cases of high grade, invasive sarcomas (osteosarcoma, hemangiosarcomas).

 

<I style="mso-bidi-font-style: normal">Tibia:  Unlike the foreleg there is not a comparable anatomic fascial structure on the tibia.  Cancer on the medial tibia is virtually on the cortical surface of the tibia because there is no muscle medially.  Resections in this area are problematic due to the lack of fascia or subcutaneous tissue.  Removal of the superficial fascia of muscles that are in continuity with the cancer can be performed on the lateral side only.  Removal of the periosteum alone may be effective in some cases on the medial surface of the tibia.

 

Cancer overlying the tibia possibly may be optimally treated with lower doses of surgery (reducing the mass to microscopic disease) followed by radiation therapy to preserve the limb.  This is now a common approach in limb preservation on the human side.  Unfortunately, radiation therapy is not readily available to many veterinary patients.  This will require surgery to play an important role in these cases.  Limb amputation still remains a viable and well tolerated procedure for most patients.

 

<I style="mso-bidi-font-style: normal">Ventral and Lateral Abdominal Wall:  Cancer in this location may be mast cell tumors, cutaneous carcinomas, mammary cancer, or soft tissue sarcomas.  The external rectus sheath of the ventral abdominal wall is dispensable to some extent.  This structure provides a tough barrier to cancer invasion, the deep surface of which will be a clean margin in most cases.  A large defect of this fascia can be closed primarily by apposing the remaining edges of fascia.  If the defect produced after tumor resection is too large to close directly, then deeper musculature is removed to achieve direct closure of the fascia.  Body wall integrity requires that the fascia be apposed.  The muscles alone will not provide adequate strength.  On the lateral body wall the external and internal abdominal oblique muscles and their associated fascia can be used as anatomic barriers to tumor invasion.  Remove cancer completely by developing a dissection plane under these muscles deep to the cancer bed.  Other muscles in the area may often be elevated and used to close defects produced.  In some cases the defect is so large that polyproplyene mesh is required for reconstruction. 

 

<I style="mso-bidi-font-style: normal">Dorsum of the Trunk:  There is liberal epaxial fascia over most of the dorsal aspect of the body.  This is relatively redundant and removal induces little morbidity.  Always take advantage of this barrier to tumor invasion to accomplish clean margins.  Removal is easy and circumvents the 3cm deep rule.  Simply close subcutaneous tissues and skin.  Deeper layers of muscle will provide all the mechanical support necessary for spinal integrity. 

 

<I style="mso-bidi-font-style: normal">Thoracic Wall:  The latissimus dorsi is a broad, fan like muscle covering large sections of the lateral chest wall.  Invasive cancer superficial to the latissimus dorsi may be completely removed by dissecting deep to this large muscle.  Functional morbidity is minimal.  The superficial and deep pectoral muscles, ventrally, may also be used in the same fashion.  Dorsally the fascia of the epaxial musculature may be removed without functional impairment.  Removal of vaccine associated sarcomas in the dorsal scapular region requires removal of much of the dorsal musculature.  The cutaneous muscle is very thin and does not function as a barrier to cancer invasion. 

 

<I style="mso-bidi-font-style: normal">Lateral Thigh:  There is a layer of thick fascia on the lateral surface of the biceps femoris, which can be removed.  Removal of this fascia exposes raw muscle surface which can be closed with subcutaneous tissue and skin.  Most other muscles of the hind leg have superficial fascia that can be removed without compromise.  In some cases removal of a partial or total muscle belly can easily be performed.  In most situations there are synergistic muscles to maintain function.

 

Tumors have three dimensions — length, width and depth.  Depth is the most difficult to accurately assess in many cases.  Don’t underestimate this dimension when planning cancer resection.  Once estimated, plan the deep aspects of the resection based on this evaluation.  Determine the definitive histologic diagnosis and grade (if applicable) before performing surgery.  This will tell you the <I style="mso-bidi-font-style: normal">proper dose of surgery to apply to the case.  Preoperative biopsies are easily procured on an outpatient basis by local anesthesia and Tru-cut biopsy technique.  When you have the diagnosis, retreat to your office, access information about the biologic behavior and plan your attack <I style="mso-bidi-font-style: normal">or retreat! This information will also tell you where else to look for systemic disease before surgery, i.e., lungs, liver, lymph nodes etc.  Prior to any surgery, attempt to find any metastatic disease that would preclude the surgical procedure.  Radiographs are only so good at finding metastatic disease so do realize their limitations in finding microscopic disease.  Very importantly, consider the tumor type in the surgery planning.  Plan ahead after review of the local anatomy and barriers to tumor invasion.  Following these principles will increase success in surgical oncology. 

 
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