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When my dog Sam underwent his first treatment for cancer at New York City’s prestigious Animal Medical Center, no fewer than five mast cell tumors were removed from his handsome physique. Few would call Sam handsome now, with his Frankenstein-esque, 8-inch-long scars on his neck, back, and hind leg.

What is calcinosis?
Calcium deposits in the skin have a variety of causes, usually of minor significance in the young but indicating serious disease in some older animals.

What types of treatment are available?
The standard treatment for almost all cancers is surgical removal of the lump, sometimes with part or all of the affected organ. Other treatments (special types of surgery, radiation treatment or drug treatment (chemotherapy) are not suitable for all cancers. Before selection or advice on these alternative treatments, there must be an accurate diagnosis of the cancer type and its extent in the animal. Cancer treatments often have significant side effects and many are available only at specialist centers, or are still under development for use in animals.

What are connective tissue and nerve tumors?
All tissues and organs of the body may develop cancer (an abnormal overgrowth of their constituent cells). Every organ (liver, lungs, spleen, kidneys and so on) contains a supporting framework of fibrous connective tissue as well as nerves to relay information to and from the brain. Most organs also contain muscle tissue and special cells (histiocytes or macrophages) whose function is to clear debris. Cancers of these tissues can therefore occur anywhere in the body.

Histiocyte biology
Langerhans cells were first recognized under the microscope in 1868 by a medical student, Paul Langerhans. These cells are members of the histiocyte group, which are part of the body’s immune surveillance system. They take up and process foreign antigens, such as pollens and viral, bacterial and fungal microorganisms.

What is this lump?
Cysts are hollow spaces containing liquid or solidified secretion. A few cysts form within cancers but only non-cancerous cysts are considered here.

What is cytology?
Cytology is the microscopic examination of cell samples.

Cutaneous (reactive) histiocytosis is an uncommon condition of dogs. The condition is poorly described in the scientific literature and has various grades all of which may be found in one animal. Other names include "sterile" granuloma/pyogranuloma syndrome. It is a non-cancerous proliferation of mixed reactive cells, predominantly histiocytes but also including white blood cells (neutrophils) and lymphocytes.