Table of Contents
Rissi and Oliveira (2022) reviewed the diagnostic approach to categorizing round cell tumors in the skin of dogs.
Rissi DR, Oliveira FN. Review of diagnostic histologic features of cutaneous round cell neoplasms in dogs. J Vet Diagn Invest. 2022; 34: 769-779.
Cutaneous histiocytoma
Cutaneous Invasive histiocytoma
Occasionally or rarely, a histiocytoma develops in a dog and it is aggressive and or metastasis to a lymph node. These are called Invasive Histiocytomas. As with histiocytomas in general, they have an immunohistochemical profile that is typical of a Langerhans cell (E cadherin+, Iba-1+ , CD18+) and negative for macrophage markers (CD11d and CD204). In the case reported by Fernandez at al (2020), the histiocytoma of Langerhans cell origin invaded around the external auditory meatus.
Faller M, Lamm C, Affolter VK, et al. Retrospective characterisation of solitary cutaneous histiocytoma with lymph node metastasis in eight dogs. J Small Anim Pract 2016; 57: 548–552.
Fernandez M, Boudreaux BB, Wilson L, Moore PF, Rademacher N, Pucheu-Haston C. Invasive histiocytoma in the ear canal of a dog. Vet Dermatol. 2020; 31: 317-e80.
This is the most common form of lymphoma in dogs. It typically affects older dogs, causes pruritis from direct stimulation of intraepidermal nerve fibres, erythema, plaques and nodules, and ulceration
Prognosis
Dettwiler et al (2023) reported on the outcome of 176 cases. Median survival was 95 (1-850) days. Those given chemotherapy lived 4 times longer and 2 times longer when treated with prednisolone. Those with stable disease lived longer. There was an increased risk of death when the panniculus was involved. Mitotic count of 7/HPF or above and large cells (>10um) had a poorer prognosis.
Dettwiler M, Mauldin EA, Jastrebski S, Gillette D, Stefanovski D, Durham AC. Prognostic clinical and histopathological features of canine cutaneous epitheliotropic T-cell lymphoma. Vet Pathol 2023; 60: 162-171.Mast cell tumors
Dermal mast cell tumors
Subcutaneous mast cell tumors
Subcutaneous mast cell tumors arise entirely in the subcutis. They were traditionally combined with dermal mast cell tumors, although some studies excluded them, including the Patniak et al () grading paper.
Prognosis
In general, the majority of subcutaneous mast cell tumors have a favourable outcome. The median disease free interval is not reached.
Gill et al (2020) found that 3 of their 43 dogs died of mast cell related disease.
Newman et al (2007) evaluated 53 cases from a referral centre. Metastasis was in 6 dogs. No histologic parameter was related to outcome.
Thompson et al (2011) evaluated 306 dogs and like other studies, the survival was high, mast cell related deaths were low (27 cases 9%) and reoccurrence was low despite cells at the margins.
Marconato et al (2023) found that 15 of 43 dogs had lymph node metastasis (HN3). These dogs were all treated with regional (but not sentinal) node removal, and those with nodal metastasis were given vinblastine; there was no difference in prognosis with lymph node metastasis. Cases were from referral centers, 17 had abnormal lymph nodes, so there is a selection bias and may not represent the usual metastatic rate of primary practice. 8 dogs had tumor progression with 7 having recurrence. 5 had further nodal involvement. 9 dogs had tumor related death.
Treggiari et al (2023) examined 52 subcutaneous mast cell tumors and 22 were given chemotherapy. Mitotic count and multinucleation is predictive. Those given chemotherapy did worse. 13 of the 22 treated dogs had HN2 or HN3 nodes
Gill V, Leibman N, Monette S, Craft DM, Bergman PJ. Prognostic Indicators and Clinical Outcome in Dogs with Subcutaneous Mast Cell Tumors Treated with Surgery Alone: 43 Cases. J Amer Anim Hospl Assoc 2020: 56: 215-225.
Marconato L, Stefanello D, Solari Basano F, et al. Subcutaneous mast cell tumours: A prospective multi-institutional clinicopathological and prognostic study of 43 dogs. Vet Rec. 2023; 193: e2991
Newman SJ, Mrkonjich L, Walker KK, Rohrbach BW. Canine Subcutaneous Mast Cell Tumour: Diagnosis and Prognosis. J Comp Path (2007) 136: 231-239.
Thompson JJ, Pearl DL, Yager JA, Best SJ, Coomber BL, Foster RA. Canine Subcutaneous Mast Cell Tumor: Characterization and Prognostic Indices. Vet Pathol 2011
Treggiari E, Valenti P, Porcellato I, Maresca G, Romanelli G. Retrospective analysis of outcome and prognostic factors of subcutaneous mast cell tumours in dogs undergoing surgery with or without adjuvant treatment. Vet Comp Oncol. 2023; 21: 437-446.
Cutaneous mastocytosis (Mastocytosis in skin)
Systemic mastocytosis
The skin can be affected in systemic mastocytosis. Systemic disease affected bone marrow, organs apart from skin and the skin. Some prefer the term 'mastocytosis in skin' for the skin only disease. Mastocytosis with involvement of bone marrow and skin is systemic mastocytosis.
Mastocytosis in skin
Wyatt et al (2024) reported on 11 dogs with MIS. They were all multifocal - nodular and papular. One has mastocytaemia.
They developed disease at 2 years, with a median of 4 years.
4 of 11 had no lesions after 2 years. 6 were lost to followup
Diffuse cutaneous mastocytosis
Maculopapular cutaneous mastocytosis
This is often called urticaria pigmentosa from the human disease. They are usually well differentiated tumors that disappear with time
There are case reports of urticaria pigmentosa like disease in dogs (Pariser and Gram, 2015)
Pariser MS, Gram DW. Urticaria pigmentosa-like disease in a dog. Can Vet J. 2015; 56: 245-248.
Wyatt EK, Affolter V, Borio S, et al. Mastocytosis in the skin in dogs: A multicentric case series. Vet Comp Oncol. 2024; 22: 136-148
Plasma cell tumors
Plasmacytoma
Solitary cutaneous plasmacytoma
HistologyThe classic appearance of these tumors is a well circumscribed round cell tumor of the deep dermis with a zone of dermal collagen between the mass and the epidermis (Grenz zone). The cells resemble plasma cells usually, especially at the periphery. Mitoses are common and some large cells are present.
In a small number of cases, the cells form packets with hollow centers or centers filled with blood - giving a glandular or thyroidal appearance. McHale et al (2018) called this divergent pseudoglandular configuration.
Ehrensing and Craig (2018) found that 21 of the 134 tumors (15.7%) had neoplastic cells within adjacent vessels. Vascular invasion was more common in tumors of the distal limbs (37.0%) compared to other locations (11.2%). This was not prognostically significant.
McHale et al (2018) reported large blood filled spaces that made the tumor look thyroidal.
Immunohistochemistry
Ramos-Vara et al (2007) examined MUM1 (Multiple myeloma oncogene 1/interferon regulatory factor 4 - MUM1/IRF4), CD79a and CD20 on 109 plasmacytomas in 107 dogs. 109 (93.5%) tumors were positive for MUM1/IRF4. The staining was nuclear with weak cytoplasmic reaction. 105 (56.2%) plasmacytomas were positive for CD79a and 21 of 108 (19.4%) cases were positive for CD20. 10 B-cell lymphomas and 1 anaplastic lymphoma were MUM1 positive.
Ehrensing G, Craig LE. Intravascular neoplastic cells in canine cutaneous plasmacytomas. J Vet Diagn Invest. 2018; 30:329-332
Ramos-Vara JA1, Miller MA, Valli VE. Immunohistochemical detection of multiple myeloma 1/interferon regulatory factor 4 (MUM1/IRF-4) in canine plasmacytoma: comparison with CD79a and CD20. Vet Pathol. 2007; 44:875-84.
McHale B, Blas-Machado U, Oliveira FN, Rissi DR. A divergent pseudoglandular configuration of cutaneous plasmacytoma in dogs. J Vet Diagn Invest. 2018; 30: 260-262.
Cutaneous Plasmacytosis
Maculopapular cutaneous plasmacytosis
Boostrom et al (2017) reports on 21 dogs with multiple cutaneous plasma cell tumors. They were older dogs (3-12 years, median 8.5). 14 of them had more than 10 lesions. Goldens and Labrador retrievers were 8 of the 12. 6 had lymph node involvement at diagnosis. 9 were alive after 519 days.
Boostrom BO, Moore AS, DeRegis CJ, Robat C, Freeman K, Thamm DH. Canine Cutaneous Plasmacytosis: 21 Cases (2005-2015). J Vet Intern Med. 2017; 31: 1074-1080.Diffuse cutaneous plasmacytosis