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The most important factor affecting the outcome of patients with invasive cancers is whether the tumor has spread, either regionally (to regional lymph nodes) or systemically. However, a proportion of patients with no evidence of systemic dissemination will develop recurrent disease after primary 'curative' therapy. Clearly, these patients had occult systemic spread of disease that was undetectable by methods routinely employed (careful pathological, clinical, biochemical and radiological evaluation). In addition, the success of adjuvant therapy is assumed to stem from its ability to eradicate occult metastases before they become clinically evident [1]. Therefore, methods for the detection of occult metastases in patients with the earliest stage of cancer, i.e., prior to detection of metastases by any other clinical or pathological analysis, have received a great deal of attention.

Immunocytochemical methods offer a new dimension for cytopathology in the diagnosis, prognosis and biology of neoplastic diseases. This concept is illustrated with particular respect to the immunodetection of bone marrow micrometastases and the role of cytologically demonstrable functional parameters in prognosis and therapy planning. A future role for the polymerase chain reaction (PCR) in this diagnostic sphere is proposed.

Numerous studies in man have shown that the assay of tumour markers in the blood and urine seldom yields sufficient forewarning of the development of metastatic disease. Accordingly, alternative approaches have been sought for their earlier detection. The deployment of immunological probes, both in vivo in the form of radioimmunolocalisation and in vitro using immunocytochemical methods at a histological level, is under active study. At present the latter method appears capable of detecting micrometastases in the bone marrow in subjects with breast cancer.

Many biochemical indices are purported to have clinical utility in the detection and management of neoplasia. Experience gained during the past decade tends to indicate their having a more important role in the detection and monitoring of metastases than of the primary lesion. From this present review of some of the commoner human tumours, it is concluded that such marker substances are important adjuncts in the management of germ cell and certain endocrine and endocrine-related tumours. The carcinoembryonic antigen (CEA) provides a marker for many gastrointestinal cancers, but there are no presently available substances with clinical usefulness for either breast or lung neoplasms. Alternative approaches to the detection of metastases are also presented. The particular use of antibody probes at an immunohistochemical level has been claimed to be able to detect micrometastastic disease in bone marrow or tumour-related monoclonal antibody probes may have application to other cancers in the future.

The evolution of metastatic colorectal cancer in patients who have had surgical treatment for a primary lesion was studied in relation the progressive changes in the blood levels of carcinembryonic antigen (CEA), to gamma glutamyl transpeptidase (GGT) and routine liver function tests (LFTs). Involvement of the liver could ofter be reliably predicted many weeks in advance of clinical diagnosis while metastases to other sites were less likely to be detected early by this test. The association of the extent of disease with the patterns of biochemical changes is discussed with reference to several illustrative examples.

Serial estimations of plasma carcinoembryonic antigen (C.E.A.) levels have been carried out in 220 patients with colorectal carcinomas who had potentially and apparently curative surgery. In a two-year follow-up period 53 patients developed recurrences or metastases. In 36 of these patients sustained rises in plasma C.E.A. titres occurred synchronously with or between three and 18 months before the clinical detection of recurrences or metastases. The use of serial plasma C.E.A. assays is therefore recommended as an additional diagnostic aid for the earlier detection of recurrent or metastatic colorectal carcinomas.

Of 312 patients presenting with breast cancer to a single clinic, 297 were screened for metastases in skin and nodes, bone, marrow, liver and lungs, using standard clinical, radiological scanning and cytological techniques. Thirty-four patients were found to have overt metastatic disease using these tests. Metastases were demonstrable on chest X-ray in 6.1% of the entire group of patients, on the bone scan in 4.2%, liver scan in 1.5%, liver ultrasound in 1.2% and in the bone marrow in only a single patient; 3.8% had contralateral or supraclavicular lymph node metastases or skin metastases. Twenty-eight of these 34 patients (82%) with overt metastases would have been classed as metastatic had only chest X-ray and clinical examination been carried out.A survey was then carried out to determine when tests for bone and liver metastases became abnormal. Bone scan and skeletal survey results were reviewed in 58 patients, 22 of whom had developed skeletal metastases and all of whom had regular skeletal scintigraphy carried out. Sixteen of 20 (80%) scans carried out within six months of the development of skeletal deposits were abnormal compared with 4 of 19 (21%) scans at the same follow-up time in those who failed to develop metastases, but few patients showed definite evidence of bone metastases on scanning prior to radiological metastases. Fifty-one patients who were found to have liver metastases at post-mortem were reviewed and most showed progressively rising alkaline phosphatase before death but only 11 of 57 (19.2%) and 14 of 50 (28%) had positive liver scintiscans and liver ultrasound examinations respectively from 3-12 months before death.

A variety of monoclonal antibody probes to the human breast have been prepared by various groups of workers. These probes are revealing hitherto unrecognized biological and biochemical differences in both normal and neoplastic breast cells. Further study is needed, however, in order to understand fully the significance of these differences. In the meantime, the use of immune probes can improve our ability to detect disease at an earlier stage in sites such as the bone marrow, and may be heralding a new era in the detection and treatment of disseminated breast cancer.

23 (60%) of 38 human breast carcinomas had significant in-vitro osteolytic activity. All patients presenting with bone metastases or hypercalcaemia had active tumours. Over a subsequent three-year follow-up period, bone metastases did not develop in any of the 15 patients with inactive tumours, and metastases at other sites developed in only 2. Of the 23 patients with active tumours, 7 either had, or have since developed bone metastases; in 4 of these hypercalcaemia also developed. 14 tumours, chosen at random, were tested for in-vitro osteolytic activity in the presence and absence of aspirin, which inhibits prostaglandin synthetase. The activity of 8 of the 9 osteolytically active tumours was significantly, though not completely inhibited by aspirin. Although the number of patients is limited, these results indicate that the in-vitro osteolysis assay may detect substances, perhaps including prostaglandins, produced by breast tumours which affect prognosis and contribute to the subsequent formation of bone metastases.

Walker carcinosarcoma cells cause in vitro osteolysis which may be inhibited by aspirin. In the rat, this tumour produces osteolytic bone deposits and hypercalcaemia, both of which can be prevented by aspirin and indomethacin, whereas soft tissue tumour deposits are unaffected by these drugs. Some human breast tumours cause in vitro osteolysis which may be inhibited by aspirin.

Single cells from mammary carcinoma infiltrating bone marrow can be detected in marrow aspirates using immunocytochemical stains for epithelial membrane antigen (EMA). This technique has been used to examine marrow aspirates taken from multiple sites from 24 patients at surgery for breast cancer. Ten of these patients had EMA-positive cells in their marrow, while 32 marrow samples from patients who did not have carcinoma were negative. These results have been combined with those obtained by taking aspirates from single sites from 47 breast patients without known skeletal deposits. Follow up showed that the patients with EMA-positive cells in their marrow developed bone metastases at a significantly faster rate.

Immunocytochemical methods can be used to demonstrate tumor products and antigens at the cellular level. This approach facilitates the classification of tumors and the detection of small metastatic tumor foci in biopsy material from various sites including the bone marrow.

Of ten tumour markers measured every 3 months after mastectomy in patients with apparently localised primary breast cancer, plasma levels of alkaline phosphatase, carcinoembryonic antigen, and gamma-glutamyl transpeptidase were the most useful in detecting metastatic disease. With these three tests a "lead interval" of 3 months or more was obtained in about half the 23 patients who developed overt metases. Clinical examination, chest X-ray, and these three markers proved the most useful combination of tests in screening for metastases, since at least one test was abnormal in 46 of 47 patients at the time of the development of metastases as judged by more detailed physical tests.