Page 773 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 33 Hematopoietic Tumors 751

monomorphous blastic and polymorphous blastic cell types; systemic disease. 850 Systemic chemotherapy is therefore indicated
however, no prognostic significance has been observed after clas- for dogs with cutaneous plasmacytosis; approximately three-quar-
ters of 14 cases experienced objective responses to either melpha-
sification, although it has been suggested that the polymorphous-
VetBooks.ir blastic type may act more aggressively in the dog. 774,852,859,880 A lan or lomustine and median progression-free and overall STs were
153 and 542 days, respectively.
850
divergent pseudoglandular histologic subtype has been reported
EMPs of the trachea, liver, and
in a small number of dogs that may be confused with epithelial uterus have also been reported in dogs, and all had a benign course
neoplasia. 851 Intravascular tumor cells were observed in 16% after local resection. 864–866 Successful therapy with melphalan and
of cutaneous plasmacytoma samples in one report, but this was prednisone has been rarely applied for a local recurrence or incom-
not found to correlate with outcome and most were behaviorally plete margins in dogs and cats. RT has been used infrequently for
benign. 783 A different classification was proposed for EMP in cats cases that are not surgical candidates, including the application of
based on percentage of plasmablasts, and some prognostic impor- strontium-90 plesiotherapy for lingual plasmacytoma in a dog. 894
tance has been documented. 786 In the case of poorly differentiated Surgery is recommended, in combination with RT, for those cases
plasmacytic tumors, IHC studies, directed at detecting immu- of SOP in which the lesion results in an unstable, long bone frac-
noglobulin, light and heavy chains, MM-1/interferon regulatory ture (see Fig. 33.25), or the patient is nonambulatory from neu-
factor-4 (MUM1/IRF4), and thioflavin T, may be helpful in dif- rologic compromise resulting from a vertebral body SOP. In the
ferentiation from other round cell tumors. 797,857,859,882,883,887–889 latter case, spinal cord decompression, mass excision, and possi-
Of note, canine cutaneous histiocytoma (not histiocytic sarcoma) bly spinal stabilization may be necessary. 829 RT can be used alone
can be immunoreactive for MUM1 and therefore should be con- (i.e., without surgery) in those cases where fractures are stable, as a
sidered in any MUM1 differential. 853 Immunoreactivity has been palliative measure for bone pain, or in the case of vertebral SOP if
+
demonstrated for canine IgG F(ab) and vimentin. 854 A variant the patient is ambulatory and stable. Good local control is usually
2
characterized by an IgG-reactive amyloid interspersed with the achieved; however, most progress to systemic MM. 797,828,881 SOP
neoplastic cells has also been described. 861 A panel of monoclo- of the axial skeleton can be managed by excision or RT alone.
nal antibodies (recognizing tryptase, chymase, serotonin, CD1a, There is controversy as to whether systemic chemotherapy should
CD3, CD79a, CD18, and MHC class II) in association with a be initiated at the time of local therapy for SOP when systemic
histochemical stain (naphthol AS-D chloroacetate) has been advo- involvement is not documented. Systemic spread may not occur
cated for use on formalin-fixed, paraffin-embedded sections of for many months to even years beyond primary SOP diagnosis
cutaneous round cell tumors to help classify poorly differentiated in humans and dogs, and studies in humans reveal no benefit to
round cell tumors (mast cell tumors, histiocytomas, lymphomas, initiating systemic chemotherapy before progression to systemic
and plasmacytomas). 888 In addition, clonality of the immuno- disease. 807,828 Two cases of SOP in cats were recently reported;
globulin heavy chain variable region gene can be performed in one was treated with external-beam RT and one managed with
plasmacytomas and myelomas using PCR technology, and this melphalan chemotherapy and both enjoyed durable remissions of
may have some diagnostic utility in difficult cases. 762 greater than 4 years. 895 Similarly, EMP of the GI tract in humans
It is important to thoroughly stage dogs and cats with plasma- are treated most commonly by surgical excision and thorough
cytomas that are at higher risk for systemic spread if contemplat- staging of disease. Systemic therapy is not initiated unless systemic
ing local or locoregional therapy without systemic therapy. This involvement is documented. Systemic chemotherapy has been
should include bone marrow aspiration cytology, serum electro- used after gastric EMP in a cat; however, the utility of adjuvant
phoresis, abdominal ultrasound, and skeletal survey radiographs therapy in the species is unknown. 896
to ensure the disease is confined to a local site before initiation of Long-term follow-up of patients with SOP is indicated to rec-
therapy. Several, albeit rare, instances of monoclonal gammopathy ognize both recurrence of disease and systemic spread. Careful
or plasma cell leukemia have been reported in dogs with cutane- attention is given to serum globulin levels, bone pain, and radio-
ous plasmacytoma, cutaneous plasmacytosis and gastrointestinal graphic appearance of bone healing in cases of SOP. Restaging of
EMP. 850,874,890,891 Staging is likely most important in cases of disease, including bone marrow evaluation, is indicated if systemic
cutaneous plasmacytosis, SOP, and GI EMP due to their relatively spread is suspected.
high metastatic rate, but is less important for cutaneous, oral, and
colorectal plasmacytomas because of their more typical benign Prognosis for Solitary and Extramedullary
behavior. Cutaneous plasmacytosis was associated with lymph
node or abdominal viscera involvement in approximately 30% of Plasmacytic Tumors
cases; however, no cases in a large compilation had positive bone Prognosis for solitary plasma cell tumors is generally good. Cutane-
marrow aspirates and only one dog had a monoclonal gammopa- ous and mucocutaneous plasmacytomas are usually cured after sur-
thy. 850 For GI EMP (including colorectal EMP), endoscopic eval- gical excision. 774,859,893 In large compilations of cases in dogs, the
uation of the entire GI tract is recommended. A single case report local recurrence rate was approximately 5%, and nodal or distant
of the use of PET/CT imaging for extramedullary splenic plasma- metastasis occurred in only 7 of 349 cases (2%). 774,783,98,855,859,860
cytoma in a dog exists; however, its utility remains unknown. 892 New cutaneous plasmacytomas at sites distant from the primary
developed in fewer than 2% of cases. Neither tumor cell prolifera-
Therapy for Solitary and Extramedullary tion rate (as measured by Ki67 IHC), intravascular tumor infiltra-
tion/emboli in the dog, nor histopathologic grading in dogs and
Plasmacytic Tumors cats were prognostic in large compilations of cases, although it has
Cutaneous and oral plasma cell tumors in the dog are almost been suggested that the polymorphous-blastic and plasmablastic
always benign and carry an excellent prognosis after conservative type may act more aggressively in the dog and cat. 774,783,786,859
surgical excision. 774,783,853,859,860,879,893 The exception is cutane- The presence of amyloid and overexpression of cyclin D1 (prog-
ous plasmacytosis where excision is not possible due to the num- nostic in human plasmacytomas) were not shown to be of prog-
ber of lesions and the fact that 30% of cases have documented nostic value in dogs. 774 Dogs with EMP of the alimentary tract