Anal Gland Adenocarcinoma (Anal Gland Cancer) in Dogs

  • Occurrence: rarer
  • Location of illness: Abdomen/pelvis
Content
Download/Print

Anal gland adenocarcinoma is a relatively rare but aggressive form of cancer that affects the anal glands of dogs. This type of cancer can spread quickly and metastasize to nearby lymph nodes and other organs. Anal gland adenocarcinoma is often associated with the release of a hormone-like substance that leads to an increase in the calcium level in the blood. Typical symptoms then include increased thirst and increased urination. The anal glands are also known as perianal or circumanal glands, as well as “hepatoid” glands. Adenocarcinoma mostly affects male dogs of large breeds (e.g. German Shepherd) and Nordic breeds.

Tumors of the anal sac are also among the tumors in the anal region of the dog. Female dogs are more likely to be affected than male dogs. The Dachshund, Cocker Spaniel, and German Shepherd breeds appear to be particularly susceptible to these tumors.

The most important facts at a glance

Anal gland adenocarcinoma is a rare but aggressive malignant tumor of the anal sacs in dogs. It mainly affects older animals, with females being slightly more frequently affected than males. Certain breeds such as German Shepherds, Cocker Spaniels, and Dachshunds appear to be predisposed.

The clinical symptoms usually develop insidiously and include local complaints such as pain when defecating and palpable masses in the anal area. A special feature of this tumor is the frequent production of parathyroid hormone-like substances, which can lead to paraneoplastic hypercalcemia with polyuria and polydipsia.

The diagnosis is based on clinical examination, laboratory analyses, cytological and histopathological examinations, as well as imaging procedures for staging. Surgical resection with wide safety margins is the most important therapeutic measure, supplemented by radiation therapy and/or chemotherapy in cases of incomplete resection or metastatic disease.

Despite aggressive therapy, the prognosis is guarded to unfavorable, with median survival times of 1.5 to 2 years for localized disease and 3 to 6 months for metastatic disease. Close monitoring is essential to detect recurrences early and maintain the patient’s quality of life.

Research focuses on the development of improved diagnostic methods, more effective treatment strategies, and a deeper understanding of the molecular mechanisms of tumorigenesis to improve the prognosis for affected dogs in the future.

Causes

The exact causes of anal gland adenocarcinoma in dogs are not fully understood. Various factors may play a role:

  1. Genetic predisposition
    Some dog breeds appear to have an increased risk, which is due to genetic components.
  2. Interactions with sex hormones are also discussed in some animals, but
    there is still no reliable evidence of a direct connection.
  3. Chronic inflammatory conditions
    Recurrent anal sac diseases could increase the risk of degeneration, as chronic irritation and tissue damage promote cell growth.
  4. Age
    With increasing age, genetic defects accumulate in the cells, which can lead to tumor growth. Therefore, mainly dogs of middle to older age are affected.

The exact causes of anal gland adenocarcinoma are still not fully understood. As with many cancers, a multifactorial event is assumed:

Genetic factors are believed to play an important role, as certain breeds are more frequently affected. However, the molecular genetic mechanisms that lead to malignant transformation of the gland cells have not yet been researched in detail. It is suspected that mutations in tumor suppressor genes and oncogenes are involved.

Chronic inflammatory conditions of the anal glands (Sacculitis analis) could increase the risk of malignant degeneration. The repeated tissue damage and subsequent repair processes promote cell proliferation and thus increase the probability of DNA damage and mutations.

Hormonal influences are being discussed, as the gender distribution is striking. In contrast to other tumors of the anal area such as perianal adenomas, which are clearly hormone-dependent, the connection with anal gland adenocarcinoma is less clear.

Environmental factors such as carcinogens in food or the environment could also play a role, but there is no reliable evidence for this

Tumor formation occurs due to uncontrolled growth of the gland cells in the anal sacs. A specific genetic predisposition has not been clearly proven. However, certain breeds (e.g. English Cocker Spaniels, German Shepherds) are extremely associated with anal gland tumors in individual cases.

Hormonal influences: It is discussed whether sex hormones or other endocrine factors (e.g. hypercalcemia as a result of the tumor) play a role. A clear connection has not yet been conclusively clarified.

Symptoms

Rare symptoms:

The symptoms of anal gland adenocarcinoma can be subtle or non-specific at first. Typical signs are:

  • Difficulties when defecating (tenesmus): The dog often presses without passing much feces.
  • Altered feces: Ribbon-like or narrow feces if the tumor constricts the rectum.
  • Pain when sitting and sitting down: Due to pressure on the altered glands or surrounding tissue.
  • Licking or biting at the anal area: Often increased licking or chewing/gnawing if there are complaints.
  • Swelling or nodule formation: Visible or palpable nodules on the perianal region.
  • General symptoms: Loss of appetite, weight loss, weakness, apathy (especially in advanced stages).

In advanced cases, constipation, stool irregularities or even massive pain can occur if the tumor invades neighboring structures or forms metastases.

The clinical symptoms of anal gland adenocarcinoma usually develop insidiously and are often only noticed in advanced stages. This contributes to the unfavorable prognosis, as the diagnosis is often made late. The typical symptoms include:

Local symptoms in the anal area include a palpable perianal mass in the anal region, which is mostly firm and immovable. Affected dogs often show pain when defecating (tenesmus), which can lead to defecation difficulties and, in advanced cases, to constipation. Due to the pain, the animals lick the anal region more frequently.

If the rectum is constricted by the tumor, ribbon-like feces can occur. Occasionally, blood may also be observed in the feces. In advanced cases, ulcerations of the skin in the anal area can occur.

Systemic symptoms result from metastasis and/or paraneoplastic hypercalcemia. Approximately 25–50% of affected dogs develop hypercalcemia, which leads to increased thirst (polydipsia) and increased urination (polyuria). Other systemic symptoms include reduced appetite to anorexia, weight loss, vomiting, weakness and lethargy.

In the case of advanced metastasis, further symptoms can occur depending on the affected organ, such as shortness of breath in the case of lung metastases or ascites in the case of liver metastases.

Diagnosis

  • Physical examination and palpation of the anal glands
  • Clinical symptoms: Frequent licking or biting in the anal area, difficulties when defecating, pressing (tenesmus), blood or mucus on the feces, and visible or palpable nodules in the area of the anus are indicative.
  • Rectal examination: Palpation of the anal sacs provides initial indications of enlargements or hardening.
  • Fine needle aspiration or biopsy to confirm the diagnosis
  • Cytology/biopsy: Tissue samples and fine tissue examinations are used to confirm the diagnosis. Histopathology can be used to clarify whether it is an adenocarcinoma.
  • Imaging techniques such as ultrasound or CT scans to assess the spread. Ultrasound (abdomen) is used to detect possible metastases (e.g. lymph nodes, liver). X-ray (thorax) is helpful for searching for metastases in the lungs, and CT/MRI are necessary for unclear findings and for surgical planning.
  • Blood tests: Elevated calcium levels (hypercalcemia) are often associated with anal gland adenocarcinomas and can cause symptoms such as weakness, increased drinking or vomiting.

The diagnosis of anal gland adenocarcinoma requires a systematic approach and includes several diagnostic procedures:

The clinical examination begins with a thorough anamnesis, with particular attention being paid to changes in defecation and drinking behavior. During the rectal examination, the veterinarian can usually palpate a firm, painful perianal mass in the area of the anal glands. This examination should be performed with caution, as it can be painful for the patient.

Laboratory tests are necessary and include a complete blood count, a serum profile with particular attention to the calcium level, and a urinalysis. Hypercalcemia is an important diagnostic indication that is present in about one third to one half of patients.

For cytological diagnosis, a fine needle aspiration of the perianal mass is performed. The cells obtained are examined microscopically to confirm malignancy. However, a biopsy with histopathological examination is largely required for a definitive diagnosis.

Imaging techniques play a central role in diagnosis and staging. Ultrasound examinations of the abdomen are used to assess the regional lymph nodes and to search for distant metastases in the liver, spleen and other abdominal organs. X-rays of the thorax are taken to detect lung metastases. In specialized centers, advanced imaging techniques such as CT or MRI can also be used, which enable a more precise assessment of the local tumor extension and the degree of metastasis.

Staging according to the TNM system (Tumor-Node-Metastasis) is important for therapy planning and prognosis. It takes into account the size and invasiveness of the primary tumor, the involvement of regional lymph nodes and the presence of distant metastases.

Therapy

  • Surgical removal of the tumor is often the preferred treatment method.
  • Radiation therapy can be used as a complementary treatment after surgery.
  • Chemotherapy can be used in cases with metastases.

The treatment of anal gland adenocarcinoma usually requires a multimodal approach, with surgical removal of the tumor being the most important therapeutic measure.

Surgical resection with wide safety margins is the therapy of choice. Depending on the location and extent of the tumor, a unilateral or bilateral anal gland removal (saculectomy) may be necessary. In advanced tumors with infiltration of the surrounding tissue, a more radical procedure may be necessary, which may include partial resection of the rectum with subsequent anastomosis. If the regional lymph nodes are affected, a lymphadenectomy should also be performed. The operation requires considerable surgical expertise, as maintaining the continence of the anal sphincter is a major challenge.

Radiation therapy can be used as an adjuvant treatment after incomplete surgical resection or in inoperable tumors. It can help prevent local recurrence and prolong survival time. Modern techniques such as intensity-modulated radiation therapy (IMRT) enable precise irradiation of the tumor tissue while maximizing protection of the surrounding healthy tissue.

Chemotherapy is mainly used for metastatic diseases. Various protocols with active ingredients such as carboplatin, doxorubicin or mitoxantrone are used. However, the effectiveness of chemotherapy in anal gland carcinoma is limited, and its main goal is to slow down tumor growth and alleviate symptoms.

The treatment of paraneoplastic hypercalcemia is an important part of supportive therapy. It includes infusion therapy to promote renal calcium excretion, the use of bisphosphonates to inhibit bone resorption, and in some cases the administration of glucocorticoids. However, the causal therapy for hypercalcemia is the removal of the tumor.

Pain management is a central aspect of palliative care. Non-steroidal anti-inflammatory drugs (NSAIDs) and opioids can be used to improve the quality of life of affected animals. However, the potential nephrotoxicity of NSAIDs in patients with hypercalcemia must be considered in pain therapy.

Complementary therapy option to surgery or radiation therapy to control the spread.

Hypercalcemia management: Infusion therapies and special medications (e.g. bisphosphonates) may be necessary if calcium levels are elevated. Strict monitoring of electrolytes and kidney values is necessary.

Supportive measures: These include pain relievers to facilitate defecation, soft food or stool regulators, and careful wound care for operations in the anal area.

Prognosis and follow-up care

  • The prognosis depends on the stage of the disease and the possibility of complete surgical removal.
  • A locally limited tumor without metastases has a better prognosis, provided complete surgical removal is successful.
  • An advanced stage with lymph node involvement or distant metastases significantly reduces survival time.
  • The recurrence rate can be high if not enough healthy tissue was operated on or tumor cells have already spread.
  • Untreated or severe hypercalcemia can lead to organ damage (especially kidneys) and thus to a poorer prognosis.
  • For long-term survival: In the early stages, dogs can live tumor-free for several years after successful surgery. In the case of metastatic disease, a lifespan of a few months to a year can be expected, depending on the individual therapy and the aggressiveness of the tumor.

Aftercare

  • Regular check-ups are recommended after surgery or radiation therapy. These include rectal examination, imaging procedures (X-ray, ultrasound) at intervals of 3 to 6 months, and blood tests (calcium content, kidney values) to detect relapses and complications early.
  • Wound and scar care is particularly important, especially in the anal area, and can promote healing. Close monitoring prevents infections or fistula formation.
  • Adequate pain management and stool-regulating measures (fiber, soft food) are particularly important for largely maintaining the quality of life.

Prevention

There is no sure way to prevent anal gland adenocarcinoma, as the exact causes are unclear. However, regular veterinary check-ups can help detect tumors early. From middle age onwards, the anal region should be routinely palpated, especially in breeds with an increased risk such as Spaniels or German Shepherds. Abnormalities such as swelling, pain or changes in defecation must be clarified immediately. A healthy diet with sufficient fiber can support the natural anal gland emptying mechanism. Since hormonal factors are also being discussed, castration could be considered in at-risk patients. Early detection is the most important preventive approach.

Outlook on current research

Current research focuses in connection with anal gland adenocarcinomas in dogs include:

  1. Individualized therapy approaches
    • Development of molecular tests to better assess the aggressiveness of tumors and, if necessary, use targeted therapies.
  1. Improved diagnostic procedures
    • New imaging methods (3D-CT, PET-CT) for more accurate localization of tumors and metastases.
  1. Modern radiation therapy concepts
    • Studies on stereotactic irradiation or intensity-modulated radiation therapy (IMRT) to better protect healthy tissue and increase the success rate.
  1. Immunotherapy
    • Research into the extent to which the body’s own immune system can be activated to fight tumor cells. This is currently predominantly in the experimental phase, but could open up new possibilities in the future.

Research on anal gland adenocarcinoma in dogs has made important progress in recent years, although this type of tumor is less intensively researched than more common cancers due to its relative rarity:

In the field of molecular oncology, genetic and epigenetic changes that contribute to the development of anal gland carcinoma are increasingly being investigated. The identification of specific mutations or altered signaling pathways could provide new starting points for targeted therapies. Initial studies have already detected changes in genes such as TP53, KRAS, and PIK3CA, which also play a role in other carcinomas.

The development of more precise imaging techniques improves early detection and staging. Modern techniques such as PET-CT (positron emission tomography combined with computed tomography) enable a more accurate assessment of tumor extent and the degree of metastasis. This is crucial for therapy planning and prognosis.

In the field of surgical therapy, minimally invasive techniques are being researched that could enable more precise tumor resection with lower morbidity. Robot-assisted surgery and improved visualization techniques could increase surgical precision and reduce postoperative complications in the future.

Radiation therapy benefits from technological advances such as stereotactic radiosurgery and intensity-modulated radiation therapy (IMRT), which allow a higher radiation dose in the tumor tissue while maximizing protection of the surrounding healthy tissue. Studies on optimal fractionation and total dose in anal gland carcinomas are ongoing.

In the field of drug therapy, new chemotherapeutic agents and targeted therapies are being investigated. Tyrosine kinase inhibitors such as Toceranib (Palladia®), which are already used in other types of tumors, are also being evaluated in anal gland carcinoma. In addition, immunotherapy is gaining importance, with checkpoint inhibitors such as anti-PD-1/PD-L1 antibodies showing promising results in preclinical studies.

Research into paraneoplastic hypercalcemia focuses on a better understanding of the molecular mechanisms and the development of targeted therapies. The identification of the factors produced by the tumor could lead to more specific treatment approaches than the currently used bisphosphonates and glucocorticoids.

Translational research approaches, which transfer findings from human medicine to veterinary medicine, are becoming increasingly important. Since anal gland adenocarcinoma in dogs has similarities to certain human carcinomas, therapeutic approaches from human oncology could be adapted.

Frequently asked questions (FAQs)

  1. Can any dog develop anal gland cancer?
    In principle, yes, but mainly older dogs are affected. Certain breeds appear to be at higher risk, but the disease can occur in all breeds.
  2. How do I, as a dog owner, recognize that my dog has anal gland problems?
    Frequent licking of the anus, scooting (sliding the rear end on the floor), pain or abnormalities when defecating can indicate anal gland problems. If a tumor is suspected, veterinary advice should be sought.
  3. What is the risk that an anal gland adenocarcinoma will spread?
    The metastasis rate is relatively high, especially in local lymph nodes. That is why a thorough examination of the lymphatic system is so important.
  4. Can I prevent anal gland adenocarcinoma?
    Specific prevention is difficult. Regular anal sac checks, hygiene and combined treatment of inflammatory conditions can reduce the general risk, but cannot reliably prevent tumor development.
  5. Is chemotherapy well tolerated in dogs?
    Many dogs tolerate chemotherapy better than humans because lower doses are used. However, side effects can occur (e.g. vomiting, diarrhea, loss of appetite). Close monitoring by the veterinarian is crucial.
  6. What happens if the tumor cannot be completely removed?
    Then radiation therapy or chemotherapy can limit growth. Palliative treatment aims to relieve pain and maintain quality of life.
  7. How do I recognize signs of hypercalcemia?
    Symptoms may include increased thirst, increased urination, loss of appetite, vomiting, weakness, and in severe cases, cardiac arrhythmia. A blood test provides certainty.
  8. Can problems with stool control arise after the operation?
    Yes, especially if the sphincter muscle or the adjacent nerves are injured during the operation. However, an experienced surgeon tried to perform the procedure as gently as possible.
  9. Do castrations have to be performed to reduce the risk?
    A general recommendation for castration as a prevention does not exist. Anal gland cancer is not clearly hormone-dependent like other types of tumors. The decision should always be weighed individually with the veterinarian.
  10. How long can a dog with anal gland cancer live?
    This depends on factors such as stage, metastasis, general condition, and therapy. With early removal, dogs can often live symptom-free for several years. In the advanced stage, the prognosis is significantly less favorable.
Content
Download/Print