The disorders that arise from histiocyte proliferation range from benign, self-resolving lesions to malignant, life-threatening sarcomas and include a newly identified splenic and bone marrow macrophage disorder. These clinicians give you the information you'll need to readily differentiate and manage these disorders.
Figure 9. An abdominal ultrasonogram from a 3.5-year-old spayed female Bernese mountain dog with disseminated histiocytic
sarcoma. Note the 1.4-cm mass in the tail of the spleen and the moderate amount of abdominal effusion. (Photo courtesy of
Dr. Rebecca Green, DACVIM [internal medicine].)
Malignancies of histiocytic origin are aggressive and uniformly fatal, with most dogs dying of local tumor recurrence or widespread
metastatic disease.1,20-22,41-45 For dogs with localized tumors, a median survival time of five months was reported with aggressive surgical excision (amputation)
alone; most dogs succumbed to metastatic disease.20
Figure 10. An abdominal ultrasonogram of the liver of the same dog as in Figure 9. The liver is mottled, and multiple 1- to
3-cm nodules of mixed echogenicity are present throughout the parenchyma. (Photo courtesy of Dr. Rebecca Green, DACVIM [internal
T cell therapy. One small study in four dogs with disseminated histiocytic sarcoma (one dog with advanced disease and three with disease confined
to the skin and regional lymph nodes) reported successful treatment after the administration of gamma-irradiated human leukemic
T cell line, TALL-104, which possesses tumoricidal activity in a non-MHC-restricted fashion without lysing cells of normal
tissue.46 Three dogs achieved a complete response, and one dog achieved two separate partial responses. None of the dogs developed
visceral disease during the follow-up period of nine to 22 months.46 Although TALL-104 cells (which are not available for commercial use at this time) appeared to be a promising therapeutic
modality for treating canine disseminated histiocytic sarcoma, these results should be interpreted with caution given the
small size of the study population and the fact that the atypical lesion distribution (confined to the skin and lymph nodes)
in 75% of the cases is a seldomly described presentation of disseminated histiocytic sarcoma.
Table 2: Prognostic Factors for Canine Histiocytic Sarcoma
Lomustine. The evaluation of lomustine (chlorethyl-cyclohexol-nitrosourea [CCNU]) in 59 dogs with histiocytic sarcoma documented a 46%
response rate, although this response was short, with a median remission of 85 days in the dogs that responded.21 Univariate analysis revealed that anemia, hypoalbuminemia, splenic involvement, and thrombocytopenia at diagnosis were as
poor prognostic indicators for survival (Table 2). The median survival time in dogs presenting with poor prognostic factors was less than one month vs. five and a half months
for dogs presenting without clinicopathologic abnormalities.21 The overall median survival time of 106 days is not surprising given the aggressive nature of this disease. However, three
dogs with microscopic residual disease were treated with lomustine: One dog died at 568 days from original diagnosis while
the others were alive at the conclusion of the study and were censored from the survival analysis at 433 and 884 days.21 Referral to an oncologist or internist is necessary for lomustine therapy.