Histiocytic sarcoma in dogs: treatment, prognosis and clinical trials

Dogs · USA & Canada

Understanding histiocytic sarcoma

Histiocytic sarcoma is a cancer of histiocytic immune cells. In dogs it can appear as localized histiocytic sarcoma, begin in several organs as disseminated histiocytic sarcoma, or occur as the distinct hemophagocytic form. Hemophagocytic HS often involves the spleen and red blood cells and may cause worsening anemia. These forms can behave differently, so confirming the form and finding where disease is present are important parts of treatment planning. Chest and abdominal imaging are commonly used for staging, with other tests chosen according to the tumor location.

What does the prognosis look like?

HS is serious, but the outlook varies a lot. In published groups of dogs, median survival has been roughly 2–3 months for disseminated disease. Longer survival, around 13–19 months, has been reported in some published groups with particular localized forms treated aggressively, but those results should not be read as the expected outcome for every dog with localized HS. Some dogs do much better or worse than these numbers, and no statistic can predict an individual dog. The practical point is that the extent and location of disease matter greatly and time matters.

What matters next

Once the diagnosis is confirmed, the next decisions depend on whether HS is localized or disseminated, whether a localized tumor can be controlled completely, and whether systemic treatment should be discussed because HS can spread beyond the original site. If surgery has already been done, review the measured margins together with staging. Before another major treatment step, it is also worth checking whether a clinical trial requires measurable disease or limits previous treatment.

Where are you now?

The tumor is still there

If surgery is possible, ask whether it can realistically be removed with clean margins. Surgery is often the best local treatment for a removable localized tumor. If clean margins are unlikely, ask what other local-control options are reasonable. It is also worth checking trials before surgery when there is time to do so safely because some studies require a measurable tumor, biopsy, or direct treatment of the tumor. This is not a reason to delay surgery your veterinary team considers necessary.

The tumor was already removed

Get the pathology report and check the measured margin status. Clean removal can solve the local problem, but it does not by itself eliminate the risk that HS may spread elsewhere. The next questions are whether staging shows disease elsewhere and whether systemic treatment is recommended. Additional treatment to the surgical site is not automatic just because the diagnosis is HS; it depends on the margins, location and whether meaningful residual local disease is suspected.

The cancer has spread or cannot be removed

Surgery may no longer be the main decision. Ask about systemic treatment, local treatment for a tumor that is causing problems, and clinical trials that accept measurable or metastatic disease.

My dog is already in treatment

You may still have trial options. Look specifically for studies that allow previous surgery, chemotherapy, or radiation, and ask what options remain if the current treatment stops working.

If you are waiting for oncology

Waiting does not mean there is nothing to do. Ask about a cancellation list or another oncology center if the appointment is far away. Gather the pathology report and any completed staging, arrange missing staging that your veterinary team recommends, and check clinical trials before the next treatment decision. Some trials require a tumor to still be measurable or exclude certain previous chemotherapy or radiation. Checking early does not commit you to a trial; it shows what options exist before one is accidentally closed.

Questions to ask your oncologist

Is this localized HS or is there evidence that it has spread?
Is the staging we have enough, or is anything important still missing?
If surgery was done, are the margins adequate and does the site need more local treatment?
Do you recommend systemic treatment now, and what are the realistic options?
Could treatment we start now affect eligibility for a clinical trial later?

How the diagnosis may appear in the record

The report may describe localized histiocytic sarcoma, disseminated histiocytic sarcoma, or the distinct hemophagocytic form, which often involves the spleen and red blood cells. Because HS can resemble other poorly differentiated cancers, ask whether morphology and immunohistochemistry support the diagnosis. Keep the tumor block and slides available for review or trial screening.

Changes to watch for at home

Report rapid growth, new masses, lameness, breathing changes, marked weakness, appetite loss, or pale gums. Collapse, breathing distress, or profound weakness needs urgent assessment. In hemophagocytic disease, worsening anemia can be part of the cancer rather than a local tumor problem.

How it is usually treated

If the disease is localized and the tumor can be removed, surgery is usually considered for local control. Radiation may be used when surgery cannot fully control the tumor. Because this cancer has a meaningful risk of microscopic or distant spread, systemic chemotherapy is often discussed; lomustine (CCNU) is one of the drugs commonly used in dogs. Clinical trials may offer additional systemic or targeted approaches.

What can affect treatment choices

Localized versus disseminated disease, primary site, resectability, surgical margins, measurable disease, metastasis, previous treatment and overall health are the main treatment-changing factors.

Treatment options available now

7 options currently in our catalog.

Check eligibility

Phase II trametinib for dogs with histiocytic sarcoma

University of Florida · USA

Location

UF Small Animal Hospital, 2015 SW 16th Ave, Gainesville, FL 32608

Study details

Currently enrolling

What is being offered: UF's oncology master page does not currently list this study, but the direct official UF protocol page still states that it is currently enrolling. Multicenter Phase II trametinib study. Published recruitment criteria require a measurable tumor, no concurrent anticancer therapy, at least a 2-week washout after chemotherapy, and at least a 4-week washout after radiation therapy.

Who may qualify: Confirmed cancer diagnosis required; Active tumor required; Measurable; chemotherapy washout: 14 days; radiation washout: 28 days

May not qualify if: Current chemo; Current radiation

Costs / coverage: 🟡 Partially funded — the study covers trametinib, scheduled recheck examinations, research blood/tumor sampling, routine laboratory tests, thoracic radiographs and abdominal ultrasound at scheduled study visits; confirm screening and other owner-paid costs with UF.

Contact: UF Clinical Studies — complete the Study Interest Form on the official trial page; UF Oncology Staff: (352) 392-2235

Official study / enrollment information →

Quasiorganelle therapy for canine histiocytic sarcoma

Michigan State University Veterinary Medical Center · USA

Location

Michigan State University Veterinary Medical Center, 736 Wilson Rd, East Lansing, MI 48824

Study details

Actively recruiting — current MSU clinical-trials page and August 24, 2026 recruitment announcement

What is being offered: First cohort receives weakened non-disease-causing Listeria-derived quasiorganelle therapy alone; second cohort receives quasiorganelle therapy including gene therapy. Up to 5 visible lesions are allowed with summed longest dimensions under 15 cm. Weekly treatment x4, then 2 weeks off, repeated for a total 16-week treatment period. While enrolled, dogs should not live with someone pregnant or planning pregnancy.

Who may qualify: Confirmed cancer diagnosis required; Active tumor required; Measurable; Min weight kg: 20; Visible tumor; Max vcog performance status: 2

May not qualify if: Current chemo; Current steroids; Current radiation; Active wounds; Immunodeficiency; Immune mediated disease; Recent systemic antibiotics 14d; Recent immunosuppressants 14d; Recent prednisone 7d; Recent chemotherapy 14d; Recent radiation 30d

Costs / coverage: 🟢 Fully funded after enrollment. Trial-associated tests, quasiorganelle treatment, hospitalization, blood/fecal sampling, imaging and treatment of trial-related complications are covered; the initial evaluation is owner-paid.

Contact: MSU Medical Oncology Team — (517) 353-5420; cvm.oncoinfo@msu.edu

Official study / enrollment information →

Evaluation of TLR agonist Z-007 in dogs with cancer

Cummings School of Veterinary Medicine, Tufts University · USA

Location

Henry and Lois Foster Hospital for Small Animals, 200 Westboro Rd, North Grafton, MA 01536

Study details

Recruiting

What is being offered: Dog study of IV or intratumoral Z-007 for solid tumors including carcinomas, sarcomas and melanoma. Public criteria include a generally 2–7 cm repeat-biopsy-accessible tumor plus medical/laboratory requirements; no prior immunotherapy or autoimmune disease. Investigator prescreening required.

Who may qualify: Confirmed cancer diagnosis required; Min weight kg: 7; Measurable

May not qualify if: Prior immunotherapy

Costs / coverage: 🟡 Partially funded. Z-007 treatment through Day 63 and treatment of Z-007/biopsy-related side effects are covered; other owner costs should be confirmed with Tufts.

Contact: clinicaltrials@tufts.edu

Official study / enrollment information →

Palbociclib for selected progressive canine solid tumors

Auburn University College of Veterinary Medicine · USA

Location

Bailey Small Animal Teaching Hospital, 1220 Wire Rd, Auburn, AL 36849

Study details

Actively recruiting — confirmed on the institution’s current clinical-trials page

What is being offered: Dose-finding oral palbociclib treatment study for measurable progressive mammary carcinoma, SCC, histiocytic sarcoma, AGASACA or melanoma; prior cancer treatment is allowed if disease is progressing.

Who may qualify: Confirmed cancer diagnosis required; Active tumor required; Measurable; Progressive

Costs / coverage: After owner-paid initial exam/screening, up to two months of trial treatment including biopsy, rechecks, bloodwork and chemotherapy are funded.

Contact: Auburn Oncology Service — (334) 844-4690; onco@auburn.edu

Official study / enrollment information →

Compassionate-Use Protocol for Advanced Non-Resectable Tumors

UT Southwestern Veterinary Research and Oncology Clinic · USA

Location

Veterinary Research and Oncology Clinic, 5801 Forest Park Rd, Dallas, TX 75235

Study details

Current

What is being offered: Investigational therapy, chemotherapy, immunotherapy and combination approaches under a prospective compassionate-use protocol

Who may qualify: Confirmed cancer diagnosis required; Active tumor required; Min weight kg exclusive: 2.5; min expected survival weeks: 3 weeks; Adequate organ function

May not qualify if: Severe systemic disease

Costs / coverage: ⚪ Owner-paid. The protocol brochure states that owners fully pay for the study, although possible subsidies may be available.

Contact: Paige Neumann, Research Study Coordinator — 214-645-6221; VROC@UTSouthwestern.edu

Official study / enrollment information →

Pilot anti-STEAP1 CAR-T cell therapy for canine histiocytic sarcoma

University of Pennsylvania School of Veterinary Medicine — Atherton Laboratory / Ryan Hospital · USA

Location

Penn Vet Ryan Hospital, 3900 Spruce Street, Philadelphia, PA 19104, Philadelphia, PA

Study details

Open to limited enrollment — confirmed by investigator on 2026-09-29; study consent under revision

What is being offered: Autologous anti-STEAP1 CAR-T cells after bendamustine preconditioning

Who may qualify: Confirmed cancer diagnosis required; Measurable

May not qualify if: Current chemo

Costs / coverage: The prior consent form says the study covers protocol-specified diagnostic tests, procedures and treatments. Treatment of complications directly caused by study treatment is covered up to $1,000; the owner pays costs above that limit and care before enrollment, for disease progression or for unrelated conditions. Coverage may change in the revised consent form; confirm with Penn before enrollment.

Contact: Matthew Atherton, BVSc, PhD, DECVIM — mattath@upenn.edu; Penn Vet Ryan Hospital

Official study / enrollment information →

Single-fraction SABR for progressive canine lung metastases

Tufts Cummings School of Veterinary Medicine · USA

Location

Henry and Lois Foster Hospital for Small Animals, 200 Westboro Rd, North Grafton, MA 01536

Study details

Recruiting

What is being offered: Single highly focused radiation dose for dogs with 2–10 progressive pulmonary metastatic nodules. The primary tumor, regional nodes and any non-pulmonary metastases must already be controlled; progression must be documented over 6–8 weeks, and all progressive lung lesions at least 5 mm must be safely treatable. Prior systemic therapy is allowed; cytotoxic chemotherapy pauses around SABR, while tolerated targeted therapy or immunotherapy may continue with radiation-oncologist approval. Tufts prescreening is required.

Who may qualify: Confirmed cancer diagnosis required; Active tumor required; Metastatic; Measurable lung metastases; Planned radiation

Costs / coverage: 🟡 Partially funded. The study covers SABR, the one-month follow-up, adverse-event rechecks related to lung toxicity, and up to $860 toward the 2–3-month CT visit. Owners pay pre-enrollment bloodwork, chest imaging, treatment-planning CT, and diagnostic confirmation.

Contact: Tufts Clinical Trials Office — clinicaltrials@tufts.edu; owner and referring-veterinarian prescreening questionnaires on the official page

Official study / enrollment information →