Here are two more helpful PDF articles about Feline Injection Site Sarcomas:

NAVC Clinician's Brief: Feline Injection Site Sarcoma 

In this article, author Dr. Sandra Axiak DVM DACVIM (Oncology) at the University of Missouri writes:

Overall, the results for treatment of ISS are disappointing. Local control is difficult to achieve, with the best results incorporating a combination of aggressive surgery and radiation therapy. The role of chemotherapy is undefined.

The most important aspects of treatment for good results are early identification of disease and advanced imaging and surgery at a referral institution. Current research is focused on immunotherapy and targeted therapy.

Journal of Feline Medicine and Surgery: Injection Site-Associated Sarcoma in the Cat. Treatment Recommendations.

and in this helpful report, author Jane Ladlow explains:

. . . one would hope the current practice of interscapular injections will change, perhaps using the hind limbs rather than distal hind limbs as vaccination at the level of the stifle is tolerated by many cats and still allows good surgical margins with amputation if an injection site associated sarcoma develops. As a number of FISSs have also occurred following the administration of long-acting corticosteroids and long-acting penicillins, it would be good practice to avoid injecting these drugs into the scruff of the feline neck. Once this message pervades into general practice, we will hopefully improve the prognosis associated with these tumours.

FYI, The American Animal Hospital Association just released the latest Feline Vaccination Guidelines for vets. There is a special Update on Feline Injection-Site Sarcomas.

Main findings are as follows:

The Task Force believes that there is currently insufficient research to justify recommending a single vaccine type. Since injection site sarcomas are a risk, the Task Force recommends vaccination in the lower distal limbs to facilitate clean margins if surgical amputation is required.

The Task Force makes the following observations regarding vaccination:

• Neither vaccinating in the interscapular space nor decreasing vaccine volume is recommended.
• Distal limb injection is recommended to facilitate amputation with 5 cm margins in two fascial planes in the case of injection-site sarcoma (Figure 1).
• More recently, ventral abdominal subcutaneous injections have been used because of the perceived relative ease of tumor removal without the need for amputation.2 However, the need to remove two fascial planes and 5 cm margins would still necessitate aggressive tissue removal from the abdomen and abdominal cavity.
• Tail vaccination has also been reported as well tolerated and elicited acceptable serological responses to vaccination in the distal limbs.57 To facilitate 5 cm margins in the case of injection-site sarcoma, vaccinations must be administered in the distal tail, something that may not be practical for most clinicians.
• Follow the 3-2-1 rule for postvaccination swelling.1,55 Obtain incisional biopsies for appropriate diagnosis.