Apocrine Gland Tumors

Apocrine Gland Tumors

Description– Apocrine glands are the major type of sweat glands in dogs. These lesions are quite common. Golden Retrievers, Collies, German Shepherds, Old English Sheepdogs and Cocker Spaniels are reported to be highly predisposed. Around 70% of these apocrine tumors are non-malignant in nature. But the malignant ones tend to be locally aggressive and have a high potential to spread to the regional lymph nodes and lungs. 

They have been categorized into apocrine adenoma (complex and mixed), apocrine ductal adenoma, apocrine carcinoma (complex and mixed), apocrine ductal carcinoma, ceruminous adenoma, ceruminous gland carcinoma, anal gland sac adenoma and anal gland sac carcinoma by World Health Organization (WHO). 

Depending on their location, they have been classified as glandular (arising from the gland) and ductular (arising from the ducts). Malignant tumors are generally seen in older dogs. They are solitary, firm and well differentiated tumors. The nodules are generally 0.5-4cm in diameter located in the dermis (mesodermic layer of the skin) and sub-cutis (deeper part of the dermis). The inflammatory malignant tumors are poorly circumscribed. They generally appear as ulcerative plaque. These lesions are highly proliferative. Since they occur in the axillary (armpit) and inguial (situated in the region of the groin or in either of the lowest lateral regions of the abdomen) regions, they are mostly mistaken for pyotraumatic dermatitis (skin lesions made worse by biting, licking, constant chewing or scratching).

Types of apocrine sweat gland carcinomas:

Apocrine adenomas (complex and mixed)– If the lesions are apocrine adenomas the clinical signs consist of lumps or soft bulges above the neighboring skin. Some lesions are multilobulated and cystic. The lobules are filled with a clear fluid. The cysts also have fine interlobular separations of connective tissue. They are common in the dogs. Breeds between 8-11 years have a higher incidence. Lhasa apso, Old English sheepdog, Collie, Shih tzu and Irish setters are highly predisposed. No sex predilection has been noted. They mostly arise on the head and neck. They grow slowly and there is no chance of recurrence following surgical extirpation. 

Apocrine ductal adenoma– This is a non-malignant lesion. These tumors develop on the head, thorax, abdomen and back. Apocrine ductular adenomas occur in dogs in the age group of 6-11 years. They are found within the deep dermis and the sub-cutis and are well-differentiated. They are multilobulated and the tumor may consist of cysts of different sizes. These tumors are also slow growing.

Apocrine carcinoma (complex and mixed)– In apocrine carcinomas, the lesions have different clinical presentations. The tumors are generally nodular, intradermal, and sub-cutaneous masses of variable sizes. They can be diffuse, ulcerative, erosive dermatitis that is often referred to as inflammatory carcinoma. The nodules are of various sizes. They vary from less than 1cm to many centimeters in diameter. It appears as an expansile skin tumor that aggravates in a centrifugal manner (aggravating in a direction away from the axis or center from a central focus of ulceration. There might be severe edema. Fibrosis (formation or development of excess fibrous connective tissue) is generally observed at the periphery of the masses. They generally occur in the inguinal and axillary areas. Their growth is quite variable. Inflammatory carcinomas aggravate with a lightening speed and metastasize to regional lymph nodes and lungs. However, complex and apocrine carcinomas generally grow slowly and have a diminished metastatic potential.

Apocrine ductal carcinoma- They are poorly differentiated and very aggressive in nature. It is often ulcerated and proliferative at the periphery. They usually grow slowly and surgical extirpation is the treatment of choice. These tumors do not have a high metastatic potential.

Ceruminous adenoma– It is a non-malignant lesion. It is found in the age group of 4-13 years. Dogs at an increased risk include Cocker spaniel and Shih tzu. They are more common in the age group of 5-14 years. Cocker spaniels are at an increased risk. They are found within the ear canal and also the vertical ear canal. They tend to be exophytic (growing outward). Ulceration and secondary infection are common. In Cocker spaniels which have a higher incidence, it is very difficult distinguishing non-malignant neoplasms from the hyperplastic polypoid otitis externa (neoplastic inflammation of the outer ear and ear canal). These lesions generally have a dark brown appearance. Although ceruminous adenomas are slow growing, they cannot be surgically excised. Therefore ablation (removal of the material from the surface of an object by vaporization, or other erosive processes) of the ear may be necessary.

Ceruminous gland carcinoma– These tumors are relatively common in dogs. Dogs between 5-14 years of age have a higher incidence. Cocker spaniels are highly predisposed. Castrated (spayed) male dogs have a predilection for developing ceruminous carcinomas. They are usually proliferative, erosive and ulcerative growths. But they do not invasive and they rarely ruin the cartilage of the ear canal. It infiltrates the dermis and lymphatics (network that contains a clear fluid called lymph) and metastasizes to the parotid lymph node (lymph nodes found near the parotid gland). Surgical extirpation results in total ablation of the ear.

Diagnostic techniques – Like any other cancer, the diagnostic techniques consist of a fine needle aspiration for microscopic examination of cell samples also called ‘cytology’. But histopathology is more important since the microscopic examination of specially prepared and stained tissue sections offers a better diagnosis. This is done at a specialized laboratory where the slides are examined by a veterinary pathologist. This information helps in determining the prognosis. It is also useful in deciding the course of action. Histopathology also rules out the presence of other cancers.

Treatment– The treatment of choice for sweat gland and ceruminous gland adenocarcinomas is complete surgical excision. If it is a neoplasm of the ear canal, complete ear ablation may be necessary. 

If the margins of the incision are free of tumor cells no additional treatment is required. But if surgical extirpation is not possible, vets opt for curative-intent radiation therapy since most of these tumors respond well to radiotherapy. 

Prognosis– Prognosis is sorely dependent on histopathological findings.