Carcinomas

Colorectal carcinoma is the fourth most common variety of malignant tumour found in women, and its frequency in men is surpassed only by carcinoma of the bronchus and stomach. Overall, it is the second most common carcinoma in the Western countries, with approximately 18 000 patients in the UK dying per annum. The rectum is the most frequent site involved.

Origin

In many cases, operation specimens show that in some part of the bowel that has been removed, in addition to the carcinoma, there are one or more synchronous adenomas or papillomas, proof indeed that adenoma and papilloma of the rectum are precarcinomatous conditions. In approximately 5 per cent of cases, there is more than one carcinoma present. It is now believed that most rectal cancers start as an ade­noma and this is due to a series of genetic changes which progressively change the adenoma from one that is not dysplastic to one that shows severe dysplasia and finally becomes a carcinoma (the adenoma—carcinoma sequence) (Vogelstein) (Chapter 67).

Pathological histology

Three types are recognised:

well-differentiated adenocarcinoma;

averagely differentiated adenocarcinoma;

anaplastic, highly undifferentiated adenocarcinoma.

  The more malignant varieties frequently contain large numbers of mucin-producing cells. The prognosis after treatment is greatly influenced by the histological grading of the tumour (see below).

Usually these carcinomas present as an ulcer, but papilliferous and infiltrating types are common.

Types of carcinoma spread

Local spread

Local spread occurs circumferentially rather than in a longitudinal direction. Usually a period of 6 months is required for involvement of a quarter of the circumference, and 71 8 months to 2 years for complete encirclement, the annular variety being common at the rectosigmoid junction. After the muscular coat has been penetrated, the growth spreads into surrounding mesorectum, but is still limited by the fascia propria (perirectal fascia). Eventually, the fascia propria is penetrated but this occurrence is rare before 18 months from the commencement of the disease. If penetration occurs anteriorly, the prostate, seminal vesicles or the bladder become involved in the male; in the female the vagina or the uterus is invaded. In either sex, if the penetration is lateral, a ureter may become implicated, while posterior penetration involves the sacrum and the sacral plexus. Downward spread for more than a few centimetres is rare except in anaplastic tumours.

Lymphatic spread

Enlargement of lymph nodes from bacterial infection is more frequent than enlargement from metastasis, and microscopical examination is required to detect carcinomatous involvement of the nodes.

Lymphatic spread from a carcinoma of the rectum above the peritoneal reflection occurs almost exclusively in an upward direction; below that level to within 1—2 cm of the anal orifice the lymphatic spread is still upwards, hut the first halting place is in the pararectal lymph nodes of Gerota. The exception to this rule is when the neoplasm lies within the field ~ the middle rectal artery, i.e. between 4 and 8 cm from the anus, in which case primary lateral spread along the lymphatics that accompany the middle rectal vein is not infrequent.

Downward spread is exceptional, drainage along the subcutaneous lymphatics to the groins being confined, for practical purposes, to the lymph nodes draining the perianal rosette and the epithelium lining the distal 1—2 cm of the anal canal.

Metastasis at a higher level than the main trunk of the superior rectal artery occurs only late in the disease. A radical operation should ensure that the high-lying lymph nodes are removed by ligating the inferior mesenteric artery and vein at the highest possible level.

Atypical and widespread lymphatic permeation can occur in highly undifferentiated neoplasms.

Venous spread

As a rule, spread via the venous system occurs late, except in that portion of the anal canal where the anoderm is firmly adherent to deeper structures. Anaplastic and rapidly growing tumours in younger patients are much more liable to spread in this way than tumours of relatively low malignancy. The principal sites for blood-borne metastases are: liver (34 per cent), lungs (22 per cent) and adrenals (11 per cent).

The remaining 33 per cent is divided among the many other locations where secondary carcinomatous deposits are wont to lodge, including the brain.

Peritoneal dissemination

This may follow penetration of the peritoneal coat by a high-lying rectal carcinoma.

Stages of progression

As a rule, carcinoma of the rectum does not metastasise early.

Dukes classified carcinoma of the rectum into three stages (Fig. 60.21).

A  The growth is limited to the rectal wall (15 per cent). Prognosis excellent.

B The growth is extended to the extrarectal tissues, but no metastasis to the regional lymph nodes (35 per cent). Prognosis reasonable.

C There are secondary deposits in the regional lymph nodes (50 per cent). These are subdivided into C1 where the local pararectal lymph nodes alone are involved, and C2 where the nodes accompanying the supplying blood vessels are implicated up to the point of division. This does not take into account cases that have metastasised beyond the regional lymph nodes or by way of the venous system. Prognosis bad. A stage D is often included which was not described by Dukes. This stage signifies the presence of widespread metas­tases, usually hepatic. Other staging systems have been developed (e.g. Astler—Coller TNM) to improve prognostic accuracy. The TNM classification has become popular inter­nationally. T represents the extent of local spread and there are four grades, T1, T2, T, and T4, depending on whether the tumour (T) is confined to the mucosa or has penetrated the rectal wall. N describes nodal involvement and M indicates the pressure of distant metastases. Histological grading. In the great majority of cases, carcinoma of the rectum is a columnar-celled adenocarcinoma. The mote nearly the tumour cells approach normal shape and arrangement, the less malignant is the tumour. Conversely, the greater the percentage of cells of an embryonic or undifferentiated type, the mote malignant is the tumour:

Low grade = well-differentiated      11 %              Prognosis good

tumours

Average grade                                   64%              Prognosis fair
High grade = anaplastic tumours    25%              Prognosis poor

Colloid carcinoma. This type of carcinoma is present in 12 per cent of cases. There are two forms: primary and secondary; much the more frequent is secondary mucoid degeneration of an adenocarcinoma. Histologically the glandular arrangement is preserved and mucus fills the acini. This type is of average malignancy. In a small number of cases the tumour is a primary mucoid carcinoma. The mucus lies within the cells, displacing the nucleus to the periphery, like the seal of a signet ring. Primary mucoid carcinoma gives rise to a rapidly growing bulky growth which metastasises very early and the prognosis of which is very bad.

Clinical features

Carcinoma of the rectum is not uncommon early in life, and when the disease commences in youth, in spite of radical treatment, death usually results within a year. However, the adult age of presentation is above 55 years. Often the early symptoms are so slight that the patient does not seek advice for 6 months or more.

Bleeding

Bleeding is the earliest and most common symptom. There is nothing characteristic about the time at which it occurs, neither is the colour or the amount of blood distinctive; often the bleeding is slight in amount, and occurs at the end of defecation, or is noticed because it has stained underclothing. Indeed, more often than not, the bleeding in every respect simulates that of internal haemorrhoids (haemorrhoids and carcinoma sometimes coexist) and it is lamentable that, in spite of oft-repeated exhortations, the patient’s doctor sometimes fails to examine the rectum but prescribes a salve while the growth advances to inoperability (see footnote, Chapter 59).

Sense of incomplete defecation

The patient’s bowels open but there is the sensation that there are more faeces to be passed (tenesmus, a painful straining to empty the bowels without resultant evacuation). This is a very important early symptom and is almost invariably present in tumours of the lower half of the rectum. The patient may endeavour to empty the rectum several times a day (spurious diarrhoea), often with the passage of flatus and a little blood-stained mucus (‘bloody slime’).

Alteration in bowel habit

This is the next most frequent symptom. The patient may find it necessary to start taking an aperient, or to supplement the usual dose, and as a result a tendency towards diarrhoea ensues. A patient who has to get up before the accustomed hour in order to defecate, and one who passes blood and mucus in addition to faeces (‘early morning bloody diarrhoea’), is usually found to be suffering from carcinoma of the rectum. Usually, it is the patient with an annular carcinoma at the pelvirectal junction who suffers with increasing constipation, and the one with a growth in the ampulla of the rectum with early morning diarrhoea (Bruce).

Pain

Pain is a late symptom, but pain of a colicky character accompanies advanced growths of the rectosigmoid, and is due to some degree of intestinal obstruction. When a deep carcinomatous ulcer of the rectum erodes the prostate or bladder, there is severe pain. Pain in the back, or sciatica, occurs when the growth invades the sacral plexus. Weight loss is suggestive of hepatic metastases.

Early symptoms of rectal cancer

Bleeding per rectum

Tenesmus

Early morning diarrhoea

Abdominal examination

Abdominal examination is negative in early cases. Occasionally, when an advanced annular growth is situated at the rectosigmoid junction, signs of obstruction to the large intestine are likely to be present. By the time the patient seeks advice, metastases in the liver may be palpable. When the peritoneum has become studded with secondary deposits, ascites results.

Rectal examination

In approximately 90 per cent of cases, the neoplasm can be felt digitally: in early cases as a plateau or as a nodule with an indurated base. When the centre ulcerates, a shallow depression will be found, the edges of which are raised and everted; this, combined with induration of the base of the ulcer, is a frequent and unmistakable finding. On bimanual examination, it may be possible to feel the lower extremity of a carci­noma situated in the rectosigmoid junction. After the finger has been withdrawn, if it has been in direct contact with a carcinoma, it is smeared with blood or mucopurulent material tinged with blood. When a carcinomatous ulcer is situated in the lower third of the rectum, involved lymph nodes can sometimes be felt as one or more hard, oval swell­ings in the extrarectal tissues posteriorly or posterolaterally above the tumour. In females, a vaginal examination should be performed, and when the neoplasm is situated on the anterior wall of the rectum, with one finger in the vagina and another in the rectum, very accurate palpation can be carried out.

Procto-sidmoidoscopy

Procto-sidmoidoscopy will always show a carcinoma, if present — provided that the rectum is emptied of faeces beforehand.

Biopsy

Employing biopsy forceps (Fig. 60.22) by way of a sigmoidoscope, a portion of the edge of the tumour is removed. If possible, another specimen from the more central part of the growth is also obtained. Expert histological examination will not only enable the diagnosis of carcinoma to be confirmed, but the tumour can be graded as to its relative malignancy, although not always with complete accuracy.

Barium enema. Barium enema or, preferably, a colonoscopy is required if possible in all patients to exclude a synchronous tumour, be it an adenoma or a carcinoma. If an adenoma is found, it can be conveniently snared and removed via the colonoscope. If a synchronous carcinoma is present, the operative strategy will need changing.

When a stenosing carcinoma is present, it may not be possible using these investigations, especially colonoscopy, to visualise the proximal colon. However, in view of the high incidence of synchronous tumours, it is imperative that a colonoscopy is always performed either before or after surgical resection.

Differential diagnosis. When a seemingly benign adenoma shows evidence of induration or unusual friability, it is almost certain that malignancy has occurred, even in spite of biopsy findings to the contrary. On the other hand, biopsy is invaluable in distinguishing carcinoma from an inflammatory stricture or an amoebic granuloma, which simulates a carcinoma very closely. The possibility of a neoplasm being an endometrioma should always be entertained in patients with dysmenorrhoea. The possibility of a carcinoid tumour in atypical cases must be remembered. In the last four instances biopsy should establish the correct diagnosis. The solitary ulcer syndrome has already been alluded to above.