M W Van Den Brekel

The prognosis of cancer patients is determined by the radicalness of treatment: residual tumor cells will grow out and develop in manifest local recurrences, regional recurrences, and distant metastases. Classical diagnostic methods such as radiology and histopathology have limited sensitivities, and only by molecular techniques can minimal residual disease be detected. In tissue samples containing the normal tissue counterpart of a tumor, only tumor-specific markers can be exploited, whereas in other samples, tissue-specific markers can be used. At present, there are two main methodologies in use, one based on antigen-antibody interaction and the other based on amplified nucleic acids. The most commonly used nucleic acid markers are mutations or alterations in tumor DNA (tumor-specific markers) or differentially expressed mRNA (tissue-specific markers). Many reports and reviews have been published on the assessment of minimal residual disease by molecular markers, showing either positive or negative clinical correlations. One of the main reasons for these contradictory findings is the technical difficulty in finding the small numbers of tumor cells in the large number of normal cells, which necessitates sensitivities of the assays up to 1 tumor cell in 2 x 10(7) normal cells. These assays often are complex, demand considerable experience, and usually are laborious. In this review, we will address a number of the technical issues related to molecular assays for tumor cell detection that make use of nucleic acids as markers. Many difficulties in data interpretation are at least in part because of technical details that might have been solved by the incorporation of one or more appropriate controls. We hope that this review clarifies a number of these issues and help clinicians and investigators interested in this field to understand and weigh the contradictory findings in the published studies. This will help move the field forward and facilitate clinical implementation.

A definition of cut-off points for nodal size is essential to determine whether cervical lymph nodes are metastatic or not. Because the currently used size criteria are defined for random populations of patients with head and neck cancer, we set out to study whether these criteria are optimal for patients without palpable metastases in different levels of the neck We defined optimal size criteria for sonography by calculating the sensitivity and specificity of different size cut-off points. We compared the sensitivity and specificity of different size cut-off points as measured on sonograms for various levels in the neck in a series of 117 patients with and 131 patients without palpable neck metastases. A minimum axial diameter of 7 mm for level II and 6 mm for the rest of the neck revealed the optimal compromise between sensitivity and specificity in necks without palpable metastases. For all necks together (with and without palpable metastases), the criteria were 1 to 2 mm larger. Our findings indicate that the current sonographic size criteria used for random patient populations are not optimal for necks without palpable metastases, nor can the same cut-off points be used for all levels in the neck.

Imaging of the neck is important to diagnose occult lesions and stage the neck in cancer patients and, to a lesser extent, help differentiate swellings in the neck. Furthermore, extension of tumors can be depicted, although assessment of operability is not very reliable. Conventional imaging techniques, such as CT, MR imaging, and US, are rapidly evolving by improvement of spatial resolution and contrast, reduction of artifacts, and development of new contrast agents. Unreliable criteria for metastases, such as size and shape, will be replaced in the future by the depiction of the microstructure inside lymph nodes and the development of specific contrast agents. US-guided aspiration is currently one of the most accurate techniques to assess occult metastases as it overcomes the criteria used by CT, MR imaging, or US without aspiration. It should be noted, however, that approximately 25% of electively operated sides of the neck contain exclusively metastases smaller than 3 mm, limiting the sensitivity in these necks to 75% for all imaging modalities. New imaging modalities, such as immunoimaging with SPECT, thallium SPECT, PET, and fused images, are rapidly developing. Although these techniques will probably become very accurate for the staging of the neck, it is doubtful whether they will be used routinely to stage the neck because of the issues of cost and availability. Their role will probably be more in the detection of unknown primaries, distant metastases, and follow-up, after radiotherapy in case of clinical doubt.

CT and MR imaging are the main modalities for examination of laryngeal pathology. In general, MR imaging seems to be the optimal method of examination in cooperative patients, especially for evaluation of their larynx prior to an attempted partial laryngectomy. CT is recommended in patients who may have rapid breathing or coughing or if MR imaging is contraindicated. The choice between the two modalities is also determined by the experience of the radiologist with these modalities. Both techniques are comparable in delineating site and extent of pathology in fat and muscular tissue. MR imaging is more sensitive than CT in detecting pathologic involvement of the cartilages. CT and MR imaging are helpful in characterization of cartilaginous tumors and benign lesions, such as laryngoceles and cysts. CT is used to assess the integrity of the laryngeal skeleton in patients who suffered from trauma, that is, for identification of occult fractures, dislocations of cartilages, or confirmation of suspected laryngeal injuries.

In 32 patients who were suspected of having a neck lymph node metastasis from a histologically proven squamous-cell carcinoma of the head and neck (HNSCC), the diagnostic value of 99mTc-labeled (750 MBq) monoclonal antibody (1-2 mg) E48 IgG (n = 17) and its F(ab')2 fragment (n = 15) was evaluated and compared. Preoperative findings on lymph node status obtained by radioimmunoscintigraphy (RIS), computerized tomography (CT), magnetic resonance imaging (MRI) and palpation were defined per side (left and/or right side of the neck) as well as per lymph node level (I through V) and compared to the histopathological outcome of the neck dissection specimen. All 31 tumors at the primary site were visualized. RIS was correct in 201 of 221 levels (accuracy 91%) and in 38 of 47 sides (accuracy 81%). Fifteen levels and seven sides with limited tumor load were scored false-negative and five levels and two sides were scored false-positive. Sensitivity and specificity of RIS were similar to those of palpation, CT and MRI. The diagnostic value of RIS with E48 F(ab')2 or E48 IgG appeared to be similar. The present study shows that RIS with either E48 F(ab')2 or E48 IgG is as valuable as the other imaging techniques. The selective accumulation of radioactivity in tumor tissues, in combination with the known intrinsic radiosensitivity of HNSCC, justifies the development of radioimmunoconjugates for radioimmunotherapy.

The introduction first of computed tomography (CT) and then in the 1980s of magnetic resonance imaging (MRI) has resulted in numerous applications of these imaging methods to head and neck oncology. MR imaging is a rapidly evolving field, which is replacing CT in the majority of lesions of the extracranial head and neck: tumors of the skull base, paranasal sinuses, nasopharynx, parapharyngeal space, and carcinomas of the oral cavity, pharynx, and larynx. MR imaging is the method of choice for the detection and staging of skull base lesions because of its superior sensitivity in detecting small lesions and its superior accuracy in staging the lesion and narrowing the diagnostic possibilities. MRI shows the extent of tumor in the paranasal sinuses more precisely, and by multiplanar imaging it outlines intracranial extension. MR imaging has greater accuracy than CT in differentiating parapharyngeal lesions and can detail the extent of tumor tissue in squamous cell carcinoma of the oral cavity, pharynx, and the larynx more accurately. It is more sensitive than CT in showing invasion by tumor tissue into the mandible or laryngeal cartilages.

The diagnostic value of 99mTc-labeled monoclonal antibody E48 F(ab')2 (750 MBq, 1 mg) was evaluated in 10 patients with a histologically proven squamous cell carcinoma of the head and neck and with clinical evidence of cervical lymph node involvement. Preoperative findings on lymph node status obtained by radioimmunoscintigraphy (RIS), computerized tomography, magnetic resonance imaging, and palpation were defined per side (left and/or right side of the neck) as well as per lymph node level (I through V) and compared with the histopathological outcome of the neck dissection specimen. In 10 patients, all 8 known tumors at the primary site were detected by RIS. Furthermore, RIS was correct in 13 of 13 tumor involved neck sides and in 17 of 20 tumor involved lymph node levels. False-negative observations comprised 3 levels containing tumor deposits smaller than 1 cm in diameter, 2 of which were not detected by any other diagnostic modality. Palpation, computerized tomography, and magnetic resonance imaging were correct in, respectively, 13, 15, and 15 of the 20 tumor involved levels. There were 2 false-positive observations with monoclonal antibody E48 and 3 with palpation. No false-positive detections occurred with computerized tomography or magnetic resonance imaging. In two of the patients, RIS provided clinically important information which was not provided by any other diagnostic method. In one patient, recurrence of laryngeal carcinoma was established at the primary site after previous radiotherapy. In another patient, bilateral instead of unilateral lymph node involvement became apparent. These preliminary data indicate that radioimmunoscintigraphy with monoclonal antibody E48 may be helpful in the diagnosis of metastatic and recurrent head and neck cancer.