10 The haematochezic or dyschezic cancer patient

Haematochezia describes the presence of what appears to be fresh blood on the surface of, passed concurrently with, or admixed into faeces. This is obviously different to melena, which describes dark, usually black-coloured, tarry stools caused by the presence of digested blood within the alimentary tract. Haematochezia may or may not be accompanied by dyschezia (which describes the difficult or painful passing of faeces) and/or diarrhoea, but it usually indicates disease within the colon, rectum or anus. Dyschezia commonly indicates disease within the anal or perianal tissues, so it may be possible by careful observation of the clinical signs to narrow down the location of the underlying pathology but as with any other suspected condition, a thorough clinical examination and diagnostic evaluation must always be performed to accurately locate the pathology. When considering these patients from the point of view of possible neoplastic causes, the differential diagnosis list for a patient with haematochezia and/or dyschezia is shown in Box 10.1.

Box 10.1 Differential neoplastic diagnoses for a dog or cat presenting with haematochezia or dyschezia

Differential neoplastic diagnoses for a dog or cat presenting with haematochezia	Differential neoplastic diagnoses for a dog or cat presenting with dyschezia
Ileocaecal tumour (carcinoma or lymphoma most commonly) Colonic tumour (carcinoma or lymphoma most likely) Rectal polyp Anal sac adenocarcinoma Perianal adenoma	Anal sac adenocarcinoma Rectal polyp Prostatic, urinary bladder or urethral neoplasia Extraintestinal pelvic canal neoplasia (e.g. soft-tissue sarcoma or haemangiosarcoma arising within the pelvic musculature) Sacral or coccygeal neoplasia

CLINICAL CASE EXAMPLE 10.1 – A DOG WITH AN ANAL SAC ADENOCARCINOMA

Signalment

10-year-old neutered male Labrador-cross dog.

Presenting signs

Dyschezia and occasional fresh blood on otherwise normal faeces.

Diagnostic evaluation

• Actually quite bright and in good body condition

• No abnormalities noted apart from swelling in the left perineal region (Fig. 10.1)

• Digital rectal examination revealed a solid, irregular mass to be present within the left anal sac

• Serum biochemistry revealed significant hypercalcaemia (total 3.9 mmol/L, ionised calcium 1.98 mmol/L) with low-normal phosphate (1.05 mmol/L). No other abnormalities were detected.

• PTHrP was significantly elevated, confirming the hypercalcaemia to be a hypercalcaemia of malignancy

• Thoracic and abdominal radiographs and abdominal ultrasound revealed no evidence of lymph node metastases

• Ultrasound of the swelling revealed an irregular mass to be present in the region of the anal sac.

Figure 10.1 Case 10.1 The perineal swelling found in the Labrador

Treatment

• The dog was taken to surgery and the mass was excised (Fig. 10.2)

• Histopathology confirmed the mass to be an anal sac adenocarcinoma, which was then classified as being stage 2 disease (see Table 12.1, p. 123).

Figure 10.2 Case 10.1 The appearance of the mass following its resection

Outcome

The dog made a rapid and excellent recovery and his signs of dyschezia resolved. The dog was monitored by clinical examination and abdominal ultrasound 3 and 6 months postsurgery but no evidence of metastatic disease was noted. Fourteen months after his surgery he developed chronic renal failure but he sadly did not respond well to treatment for this, so he was euthanized. However, abdominal ultrasound and thoracic radiographs revealed him to still be free of metastatic disease.

Theory refresher

There are many possible neoplastic differential diagnoses for a patient presenting with haematochezia or dyschezia as Box 10.1 illustrates. It is, therefore, vitally important for the attending clinician to obtain a detailed history and undertake a thorough physical examination in every case to ensure that a correct diagnosis is reached.

Perianal adenomas (also known as ‘hepatoid tumours’) are the most common form of perianal tumour but they are usually asymptomatic and, more often than not, are found by the owners. These tumours are benign, usually being seen in older dogs, especially intact males. This gender predisposition is thought to be due to the tumour development being sex-hormone dependent in that testosterone can stimulate their development and oestrogens suppress their development (so affected females have usually been neutered). These tumours grow slowly, unlike their potentially malignant counterpart, perianal adenocarcinomas which although similar in appearance, generally grow more rapidly and therefore can cause dyschezia if they reach a reasonable size. Perianal adenomas usually respond well to castration with or without mass removal (usually recommended if there is any ulceration) with over 90% cure rates being reported. However, perianal adenocarcinomas rarely respond to castration, meaning that careful surgery attempting to obtain clean margins is required for these tumours. However, obtaining margins can be difficult due to the locally invasive nature of these tumours and also the fact that they are frequently located close to the anal sphincter. There is no clearly efficacious chemotherapy for perianal adenocarcinoma, so good surgical excision is the only recognized treatment for these tumours. In one American study, the clinical stage of the tumour had a clear prognostic significance for perineal adenocarcinoma; 60% of cases with primary tumours less than 5 cm in diameter were alive for at least 2 years after surgery but dogs with lymphatic involvement or distant metastatic disease had a median survival time of only 7 months.

Apocrine gland adenocarcinomas of the anal sacs are tumours seen relatively frequently in general practice, with their incidence being quoted as 17% of all perianal tumours and 2% of all canine skin tumours (as opposed to the tumour being considered rare in cats with apocrine gland adenocarcinoma of the anal sac only being reported in two cats). Although more common in older dogs, these tumours have been reported to occur in dogs as young as 5 years old, so a careful digital evaluation of the anal sacs is highly recommended in any dog presenting with signs of dyschezia, haematochezia or in whom perianal swelling is identified. Metastatic disease can also cause pelvic obstruction presenting as obstipation.

The main concerns for ‘anal sac carcinomas’ are their metastatic potential and also their ability to cause hypercalcaemia (approximately 25–50% of cases). Studies have suggested that between 50 and 80% of cases will have metastatic disease at the time of presentation with the iliac and sublumbar lymph nodes being the main predilection site for secondary disease. Late metastasis to the liver and lungs is a possible feature. It is also important to remember that small primary tumours can still give rise to large secondary tumours so careful disease staging is definitely required before contemplating surgical excision for this condition. Lateral abdominal radiographs and abdominal ultrasound (to evaluate the sublumbar lymph node chain and the liver and spleen in particular) really should therefore accompany left and right inflated lateral thoracic radiographs in all cases suspected to have an anal sac adenocarcinoma. If a patient is found to be hypercalcaemic, this will obviously require treatment and stabilization before surgery can be considered.

Surgical excision is the first-line treatment for anal sac adenocarcinomas but the disease-free period and survival times may be increased if adjunctive radiotherapy with or without chemotherapy is also employed. Several studies have indicated that the median overall survival time for these patients is approximately 18 months, but the TNM staging of each tumour has significant prognostic significance (see Table 12.2). Animals with metastatic disease that cannot be treated surgically have a substantially poorer prognosis than those in whom no macroscopic disease is left behind.

Postoperative chemotherapy has certainly been described and studies have looked at using both platinum-containing drugs (cisplatin and carboplatin) and also melphalan. In studies using the platinum drugs, partial remission was achieved using medical therapy alone but the response rate was low at approximately 30% and the median survival time was 6 months. However, this suggests that platinum-containing compounds do have some activity against anal sac adenocarcinomas. The work using melphalan was undertaken in Australia and describes using melphalan postoperatively (at which sublumbar lymphadenectomy was undertaken if metastases were present) with survival times of approximately 2 years being reported. However, in the author’s (RF) experience of using postoperative melphalan, survival times this long in patients with metastatic disease that even undergo metatastecomy is unusual. There may be a breed bias to these figures too, so further work is required to establish the role for chemotherapy postsurgery in anal sac adenocarcinomas but it is certainly worth considering.

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