Detection of unknown occult primary tumors using positron emission tomography

Carcinoma of Unknown Primary - an Orphan Disease?

Carcinoma of unknown primary (CUP) is an intriguing clinical finding that is defined as biopsy-proven metastasis from a malignancy in the absence of an identifiable primary site after a complete clinical work-up. CUP is a relatively common clinical entity, accounting for approximately 3-5% of all cancer diagnoses, and consists of a heterogeneous group of tumors that have acquired the capacity to metastasize before the development of a clinically evident primary lesion. Notable advances have been made over the past years in the treatment of well-defined clinical subgroups of CUP, such as women with peritoneal carcinomatosis and young adults with poorly differentiated carcinomas of midline distribution, but for the majority of patients, the prognosis still remains poor. In this review, we highlight recent advances in the diagnosis and treatment of patients with CUP syndrome, and emphasize the importance of identifying several favorable subsets of CUP, amenable to specific treatment options. In addition, we will point out novel diagnostic and therapeutic approaches which will hopefully improve both our understanding and the prognosis of this more or less neglected disease.

[Bone metastases from unknown primary. FDG-PET detection of two synchronous tumors]

A 60-year-old woman presented with noncardiac chest pain over months and negative laboratory findings. Conventional imaging methods and bone scintigraphy detected bone lesions suggesting metastatic disease from an unknown primary tumor. An 18FDG-PET scan performed to orient the search for the primary tumor found focal lesions suggesting lymphoma and identified a focal thyroid lesion and a cervical lymph node accessible for biopsy. The biopsy of this lymph node incidentally detected a papillary differentiated thyroid cancer (DTC), since the existence of a non-Hodgkin's lymphoma was confirmed after a new biopsy. After confirming the presence of a lymphoma, 18FDG-PET enabled the initial staging of the tumor, the evaluation of the response to treatment, and follow-up for detection of recurrence. On the other hand, 18FDG-PET incidentally detected a DTC.

Alternative Breast-Imaging Approaches

Although conventional breast-imaging techniques routinely include mammography and ultrasound, growing interest in other approaches, perhaps most notably MR imaging, has drawn increasing attention to exploiting the anatomic and physiologic basis for understanding breast cancer. Nuclear medicine techniques have been applied in several circumstances with the intent of approaching or defining a role for molecular imaging, exemplified by the use of F-18 fluorodeoxyglucose and positron emission tomography. Other techniques, including exploitation of additional components of the electromagnetic spectrum, have provided novel concepts that may ripen into clinical use.

Impact of PET-FDG in the diagnosis and therapeutic care of patients presenting with metastases of unknown primary

We carried out a study to evaluate the contribution of positron emission tomography with (18)F-fluorodeoxyglucose (PET-FDG) in the diagnosis and therapeutic care of patients presenting with metastases of unknown primary. PET-FDG was prospectively performed in 51 patients. The PET-FDG data were confirmed histologically or by a follow-up on average at 13 months. PET-FDG identified the primary in 24 percent of cases, and detected the presence of additional metastases in 41 percent of cases. PET-FDG led to a therapeutic modification for 12 patients (24 percent). Furthermore, the therapeutic impact seems more marked in localized forms than in the multifocal. This broad exploratory study confirms the important role of PET-FDG in the diagnosis and therapeutic management of patients with metastases of unknown primary.

Prognostic and diagnostic accuracy of [18F]FDG-PET/CT in 190 patients with carcinoma of unknown primary

PURPOSE

The aim of the study was to determine the accuracy of [(18)F]fluorodeoxyglucose (FDG) PET/CT in the search for the primary and the presence of a malignancy. The prognostic value of FDG-PET/CT information was tested.

METHODS

A total of 190 patients were retrospectively analysed: 82 with histologically proven metastases (HPM) and 108 with clinical suspicion of the presence of a malignancy (CSM). The sensitivity and specificity were determined. Overall survival was calculated to evaluate the prognostic value of the FDG-PET/CT findings.

RESULTS

In the search for the primary, the sensitivity and specificity were 62.0% and 81.9%, respectively. In the search for the presence of a malignancy, the sensitivity and specificity were 93.6% and 85.7%, respectively. Between the HPM and CSM groups, no significant difference in sensitivity and specificity was found either in the search for the primary or in the search for the presence of a malignancy. No significant difference in the sensitivity and specificity was found between 78 patients who were investigated by contrast-enhanced FDG-PET/CT and the remaining patients. A significantly shorter overall survival was found among patients with positive FDG-PET/CT findings compared with patients with negative findings (p = 0.00001); no significant difference in survival was found between the HPM and the CSM group (p = 0.770).

CONCLUSION

FDG-PET/CT imaging is very helpful in the search for the presence of a malignancy in patients with carcinoma of unknown primary syndrome. FDG-PET/CT is less accurate in identifying exactly the site of a primary. Discovery of a hypermetabolic lesion was associated with the worst survival rate.

Malignant melanoma in the 21st century, part 2: staging, prognosis, and treatment

Critical to the clinical management of a patient with malignant melanoma is an understanding of its natural history. As with most malignant disorders, prognosis is highly dependent on the clinical stage (extent of tumor burden) at the time of diagnosis. The patient's clinical stage at diagnosis dictates selection of therapy. We review the state of the art in melanoma staging, prognosis, and therapy. Substantial progress has been made in this regard during the past 2 decades. This progress is primarily reflected in the development of sentinel lymph node biopsies as a means of reducing the morbidity associated with regional lymph node dissection, increased understanding of the role of neoangiogenesis in the natural history of melanoma and its potential as a treatment target, and emergence of innovative multimodal therapeutic strategies, resulting in significant objective response rates in a disease commonly believed to be drug resistant. Although much work remains to be done to improve the survival of patients with melanoma, clinically meaningful results seem within reach.

Management of cancer from an unknown primary

Treatment of cancer is reliant on identifying the organ of origin. However, in a significant minority of cases, the primary site is never identified. This paper reviews the diagnostic work-up and therapeutic management for patients presenting with unknown primary cancer, including the role of tumour markers, conventional pathology and positron emission tomography imaging. It is important to identify atypical presentations of known tumour types, such as extragonadal germ cell tumours, lymphomas and breast cancer. The results from chemotherapy trials performed in patients with unknown primary cancer are summarised. Few trials have included > 100 patients, and most are non-randomised. There is no clear standard of care from the available data, and no trials of chemotherapy versus best supportive care have been performed. Platinum is the mainstay of treatment regimens, and from the regimens tested, a taxane seems to be among the best of the cytotoxics to combine with platinum in terms of both tolerability and efficacy. There is no data to favour a three-drug combination over a two-drug combination. To improve on existing treatment, molecular techniques may provide a means to identify the organ of origin, and/or to select appropriate targeted therapies. Further research is needed to improve knowledge on the biology of cancer from an unknown primary and to develop more effective treatment.

[Metastases with CUP syndrome]

Carcinoma of unknown primary is common, accounting for 2-6% of all cancer patients. The primary site is found in less than 25% of patients before death and frequently goes undiscovered at postmortem examination. At the time point of first diagnosis of CUP syndrome, usually more than 80% of the patients present a disseminated situation. Prognosis depends on the involved site and is unaffected by whether or not the primary site is ever found. For patients presenting with metastasis to peripheral lymph nodes, node dissection may be curative. In patients with small cell malignancies, peritoneal carcinomatosis (in women), poorly differentiated carcinomas involving external lymph nodes, mediastinum, or retroperitoneum, but without metastases to viscera or bone, objective long-term responses are possible with combination chemotherapy. For all other patients, toxic therapies are recommended only for patients with good functional status, for palliation of symptoms when they develop, and for continuous support of the quality of life.

The role of 2-deoxy-2-[F-18]fluoro-D-glucose positron emission tomography in disseminated carcinoma of unknown primary site

BACKGROUND

The authors conducted a comprehensive review of the efficacy of 2-deoxy-2-[F-18]fluoro-D-glucose positron emission tomography (FDG-PET) in the detection of primary tumors in patients with disseminated carcinoma of unknown primary site.

METHODS

Ten studies (involving a total of 221 patients) tat were published between 1998 and 2006 were reviewed. Each study evaluated the role of FDG-PET in the detection of unknown primary tumors after a conventional diagnostic workup. Although 94% of patients had a single site of metastases, the studies otherwise were very heterogeneous in the studied population, study design, and additional diagnostic workup.

RESULTS

In 41% of patients, FDG-PET detected primary tumors that were not apparent after conventional workup. In this group of patients, the overall sensitivity, specificity, and accuracy rates of FDG-PET in detecting unknown primary tumors were 91.9%, 81.9%, and 80.5%, respectively. FDG-PET imaging also led to the detection of previously unrecognized metastases in 37% of patients. Lung cancers represented 59% of the detected tumors. FDG-PET had a notably high false-positive rate (58.3%) in tumors of the lower digestive tract. FDG-PET altered the clinical management in 34.7% of patients. Most of those patients (53%) received specific chemotherapy for lung and pancreatic cancers; whereas 12% received specific therapy for breast, ovarian, and prostate cancers; and 14% underwent surgery with curative intent.

CONCLUSIONS

FDG-PET was an efficient method for detecting primary tumors that were undetected by other modalities and was sensitive for the detection of previously unrecognized metastases. FDG-PET significantly changed clinical management in approximately one-third of the patients studied.

[Positron emission tomography in head and neck squamous cell carcinomas]

18F-Fluorodeoxyglucose positron emission tomography (PET) is an imaging modality which is becoming increasingly esential in oncology, especially in the management of head and neck squamous cell carcinomas (SCC). The most common uses of the PET are listed in this thematic study: initial staging, cervical lymph node metastases from an unknown primary tumor and post-therapeutic follow-up. The advantages and drawbacks of this imaging tool are exposed here according to both our experience and data from the literature. Decision schemes are suggested for each use so as to optimize the use of this imaging modality in the management of these SCC. Other fields of application for the PET are mentioned, such as the in-progress evaluation of response to chemotherapy, the interest of this imaging tool in radiotherapy as well as current biochemical developments concerning new tracers.

Fluoro-substitution effects in deoxyfluoro-d-glucose derivatives: random conformational search and quantum chemical calculation

The effect of substitution by the fluorine atom at different positions of D-glucose was investigated by quantum chemical calculation of the low-energy conformers. These were obtained through the Random conformational search method. The geometries of conformers were optimized at the RHF/6-31(d) level, then reoptimization and vibrational analysis were performed at the B3LYP/6-31+G(d) level. Single-point energies were calculated at the B3LYP/6-311++G(2d,2p) level. The free energies of solvation in water were calculated utilizing the AM1-SM5.4 solvation model. For all substitution positions, the ring conformation does not change much, and the pyranoid 4C1 conformers are dominant, while variations in the substitution site result in different effects in the network of hydrogen bonds, anomeric effect, the solvation free energy, and the ratio of alpha- and beta-anomers.

Les carcinomes de primitif inconnu

PURPOSE

Carcinoma of unknown primary site is a common clinical syndrome, accounting for 2% of cancer patients. Diagnosis is a recurrent challenge for internists. Treatment is difficult and prognosis is still poor. This review presents one synthesis of diagnosis strategies and therapeutic trials. It envisages the interest of new molecular biology methods as well as therapeutic perspectives.

CURRENT KNOWLEDGE AND KEY POINTS

Pathologic examination completed with immunohistochemical tests, and, depending on cases, with electron microscopy, cytogenetics, and molecular biology is a key-point for diagnosis. Diagnosis work-up, based on histological type and on individualization of some clinical presentation, proceeds in three steps. Positron emission tomography is recommended when a curative treatment is planed, particularly in cases of isolated metastasis. Functional status analysed using the performance status and simple biologic parameters (serum lactate dehydrogenase, serum alkaline phosphatase) permit us to assess prognosis. Chemotherapy is offered for patients with a good general health status.

FUTURE PROSPECTS AND PROJECTS

Further evaluation of positron emission tomography, as well as cost-benefit analyses, is warranted. Further randomised trials are necessary to determine the optimal chemotherapy regimen in good-risk patients and the interest of chemotherapy in patients with poor-risk disease. Gene expression profiling and proteomic evaluation, as well as pharmacogenomic offer new investigation fields.

The current status of positron-emission tomography scanning in the evaluation and follow-up of patients with head and neck cancer

PURPOSE OF REVIEW

Functional imaging has increasingly become an important diagnostic tool for head and neck cancer and as its availability increases so will its utilization. Positron-emission tomography using the radiotracer [18F]fluoro-2-deoxy--glucose is the most commonly used functional imaging technology and it has the potential to improve the staging and detection of head and neck tumors compared with conventional imaging techniques such as computed tomography or magnetic resonance imaging.

RECENT FINDINGS

The combination of [18F]fluoro-2-deoxy--glucose and positron-emission tomography contributes valuable information in localizing a primary tumor in patients with an unknown primary and neck metastases, in the staging of primary head and neck cancer, in the detection of residual disease following definitive chemoradiation, and in the detection of recurrent disease. New technologies have been recently introduced using the combination of computed tomography and positron-emission tomography that allows exact anatomical correlation with areas of increased tracer uptake. In addition, new tracers may allow quantification of important cellular processes related to tumor proliferation or identification of tumors that may respond to certain targeted therapies.

SUMMARY

[18F]Fluoro-2-deoxy--glucose and positron-emission tomography are increasingly being used as a clinical imaging modality in the complex management of head and neck cancer. In particular, its clinical value in the evaluation of the unknown primary, and the evaluation of recurrent or residual disease, is well established and has shown to be more accurate than conventional imaging modalities.

FDG PET in patients with cancer of an unknown primary

BACKGROUND

This prospective study was undertaken to address the capacity of positron emission tomography (PET) with 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) to determine the primary tumour site of carcinomas with unknown primary site.

PATIENTS AND METHODS

Twenty-five patients with metastases from adenocarcinoma or undifferentiated carcinoma of unknown primary site (CUP) were included prospectively. For all patients, extensive imaging was unsuccessful in localizing the primary site. Patients received 370 MBq of 18F-FDG intravenously, and whole-body images were acquired 60 min after injection. All hot spots that could not be attributed to a metastatic site were considered as the primary tumour. The evaluation of FDG PET data was based on clinical and radiological outcome or surgery if indicated.

RESULTS

Twenty-four patients were eligible for analysis. All known metastases were visualized. In six patients, FDG PET showed a primary tumour site which was confirmed by follow-up or surgery. In five patients, the primary tumour site was suggested by FDG PET but not confirmed by clinical outcome. No primary tumour was found in the other patients, with a mean follow-up of 15 months.

CONCLUSION

In our series, FDG PET allowed the identification of primary tumour site in one quarter of patients with CUP (6/24). We conclude that FDG PET has a place in the initial staging of these patients.

Current use of 18F-Fluorodeoxyglucose Positron Emission Tomography and Combined Positron Emission Tomography and Computed Tomography in Squamous Cell Carcinoma of the Head and Neck

The history and physical examination, computed tomography (CT) and magnetic resonance imaging are the cornerstones for identifying new and recurrent cancers of the head and neck. The advent of positron emission tomography (PET) and combined PET/CT imaging technology is a promising development. These modalities have the potential to help stage patients presenting with head and neck cancer, identify responses to nonsurgical therapy, and allow earlier detection of recurrence in the hope of improving survival. The following paper provides a brief history of PET and PET/CT imaging. The current PET and PET/CT literature for squamous cell carcinoma of the head and neck is reviewed, and specific recommendations for its use are provided.

Update on 18F-Fluorodeoxyglucose/Positron Emission Tomography and Positron Emission Tomography/Computed Tomography Imaging of Squamous Head and Neck Cancers

This article summarizes the recent literature in (18)F-fluorodeoxyglucose/positron emission tomography (FDG-PET) imaging of head and neck cancers and extends the previous review in this area by Schöder and Yeung in the July 2004 issue of Seminars in Nuclear Medicine. Positron emission tomography/computed tomography (PET-CT) imaging is now used widely but has not been adequately evaluated for head and neck cancer. Its accuracy in initial staging is better than CT but may be similar to magnetic resonance imaging. It is not sufficiently accurate in the N0 neck to rule out nodal metastases but may be appropriate if sentinel node mapping is performed in patients with PET studies showing no nodal disease. PET imaging is beginning to be used in radiotherapy treatment planning, where it makes a significant difference by identifying malignant normal size nodes, extent of viable tumor, and distant disease. PET continues to be useful in carcinoma of unknown primary in identification of the primary site. Overall success is around 27% after all other modalities have failed. FDG-PET is being used frequently to assess response to therapy and for surveillance thereafter. The major controversy is when to image after radiotherapy or combined chemo-radiotherapy. One month seems to be too early. The ideal time seems to be 3 to 4 months to avoid both false-positive and false-negative studies. The growing use of PET-CT studies in head and neck cancer will certainly make a significant difference in the treatment and outcome in this disease.

Brain metastasis of unknown primary: A diagnostic and therapeutic dilemma

The diagnosis of a brain metastasis is usually made during the routine follow up examinations of patients with known cancer, who are under the care of oncology departments. The involvement of the neurosurgeon depends on the philosophy and referral patterns of each oncology group. Patients with brain metastases of unknown primary (BMUP) are much more likely to seek the help of a neurosurgeon or a neurologist before contacting an oncologist, because the presenting clinical features originate from the brain. BMUPs are almost equal in numbers to brain primaries and differ from regular cerebral metastases regarding their site of origin, which will remain unknown in about 50% despite vigorous investigation. The clinical picture is similar to that of primary brain tumours but they seem to show different areas of predilection in the brain parenchyma. By reviewing the literature we are presenting the epidemiology, clinical presentation, diagnostic workup and treatment plan for this group of patients.

Positron emission tomography/computed tomography true fusion imaging in clinical head and neck oncology: early experience

PURPOSE

Positron emission tomography-computed tomography (PET-CT) is a new imaging modality that provides simultaneous functional and anatomic information. Its application in head and neck oncology is still evolving.

MATERIALS AND METHODS

Five illustrative cases who were scanned with this technique are presented.

RESULTS

The clinical application and impact on clinical management are described and discussed.

CONCLUSION

Our experience indicates that PET-CT will assume a more important role than either CT, magnetic resonance imaging, or PET alone in head and neck cancer imaging.

Dual modality of 18F-fluorodeoxyglucose-positron emission tomography/computed tomography in patients with cervical carcinoma of unknown primary

OBJECTIVE

To evaluate an optimized F-18-flurodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) acquisition protocol for head and neck cancer and assess the usefulness of combined FDG-PET/CT in locating unknown primary tumors in patients with biopsy-proven cervical lymph node metastases.

SUBJECTS AND METHODS

Twenty-one patients with cervical lymph node metastases of unknown primary tumors underwent staging with FDG-PET/CT. The images of FDG-PET alone, CT alone, FDG-PET/CT read side by side and fused and FDG-PET/CT were evaluated separately by 2 physicians. Imaging results were correlated with either histology (n = 14) or clinical follow-up (n = 7).

RESULTS

On the fused FDG-PET/CT images, primary tumors were identified in 12 patients (57%); with FDG-PET alone and FDG-PET and CT read side by side 11 (52%) primary tumors were found while CT alone identified 5 (23%) primary tumors.

CONCLUSION

Our data indicate that fused FDG-PET and CT images increased the sensitivity of detecting carcinoma of unknown primary (CUP) tumors compared to CT alone, but not to FDG-PET alone or FDG-PET and CT read side by side. Hence accurate fusion of functional and morphologic data by FDG-PET/CT is a promising imaging modality in the clinical workup of patients with cervical CUP tumors.

The Utility of 2-Deoxy-2-[F-18]fluoro-d-glucose Positron Emission Tomography in the Investigation of Patients with Disseminated Carcinoma of Unknown Primary Origin

PURPOSE

A retrospective analysis of the use of 2-deoxy-2-[F-18]fluoro-D-glucose (FDG) positron emission tomography (PET) was performed in patients with histologically proven disseminated carcinoma of unknown primary tumor (CUP).

PROCEDURES

The records of 31 patients with CUP, excluding patients with isolated neck metastases, were reviewed to identify the ability of PET to detect the putative primary site (PPS) and/or to change therapeutic management.

RESULTS

In eight out of 31 cases (26%), a PPS was confirmed, either definitively (one pathologically, one radiologically) (true positive) or clinically (six cases). For three cases (10%), histological evidence of a primary tumor distant from the PPS was found (false positive). In a further seven cases (23%), the PPS remained unconfirmed, whereas for 13 cases (42%) no PPS was identified. In five out of seven patients in whom the PET suggested a high probability of having identified the primary site, the PPS was confirmed definitively or clinically. PET altered clinical management in at least 12 cases (38%).

CONCLUSIONS

PET contributed to the management of previously extensively investigated patients with CUP. Identification of a PPS and/or change in management was documented in 38% of cases, the majority of which were lung or pancreatic cancer. These findings are worthy of evaluation in a prospective study.

Functional imaging in head and neck cancer

Functional imaging has become an increasingly important diagnostic tool for head and neck cancer, and as its availability increases so will its utilization. Positron emission tomography (PET) with the radiotracer 18-fluorodeoxyglucose (18FDG) is the most commonly used functional imaging technology, and it has the potential to improve the staging and detection of head and neck tumors compared with conventional cross-sectional imaging techniques such as CT or magnetic resonance imaging. Specifically, PET contributes valuable information for localizing a primary tumor in patients with an unknown primary and neck metastasis, in the staging of untreated head and neck cancer, in the detection of residual disease after definitive radiotherapy or chemoradiotherapy, and in the detection of recurrent disease. New technologies have been introduced using the combination of CT and PET, which allows exact anatomic correlation with areas of increased tracer uptake. In addition, new tracers may allow quantification of important cellular processes related to tumor proliferation or identification of tumors that may respond to certain targeted therapies. This strategy will eventually enable physicians to tailor therapy to molecular characteristics and therefore improve outcomes for patients with head and neck cancer.

Role of 18F-FDG PET–CT imaging for the detection of an unknown primary tumour: preliminary results in 21 patients

PURPOSE

Metastatic cancer of unknown primary origin is a syndrome characterised by a poor prognosis, with a typical survival rate from diagnosis of no longer than 1 year. Only 20-27% of primary tumours are identified by conventional radiological imaging. By contrast, it has been reported that 18F-fluorodeoxyglucose positron emission tomography (FDG PET) allows the identification of 24-40% of otherwise unrecognised primary tumours. To our knowledge, the studies on this topic have been conducted using 18F-FDG PET imaging alone. The aim of this study was to evaluate the potential additional diagnostic role of fused 18F-FDG PET-CT imaging for the detection of metastatic occult primary tumours.

METHODS

The study population consisted of 21 consecutive patients with biopsy-proven metastatic disease and negative conventional diagnostic procedures. Each patient underwent a PET scan, carried out according to a standard procedure (6 h of fasting, i.v. injection of 370 MBq of 18F-FDG and image acquisition with a dedicated PET-CT scanner for 4 min per bed position).

RESULTS

18F-FDG PET-CT detected the occult primary tumour in 12 patients (57% of cases), providing a detection rate higher than that reported with any other imaging modality, including conventional 18F-FDG PET.

CONCLUSION

The favourable results of this study need to be confirmed in larger patient populations with long-term follow-up.

[The value of 18F-fluoro-2-deoxy-D-glucose positron emission tomography (18F-FDG PET) in diagnosis of neoplastic diseases]

Positron emission tomography (PET) has the ability to detect cancer based on molecular and biochemical processes within the tumor tissues. The most widely used radiotracer in oncology at this time is the glucose analogue 18F-fluoro-2-deoxy-D-glucose (18F-FDG). Like glucose, 18F-FDG is transported into cells by a glucose transporter protein and rapidly converted into 18F-FDG-6-phosphate. PET imaging with 18F-FDG is able to diagnose, stage, and restage many cancers with accuracies ranging from 80% to 90%. Responses to therapy can be identified earlier and with greater accuracy than is possible with anatomic imaging modalities. The prognostic information available through 18F-FDG PET is superior to that of conventional imaging for many cancers. The aim of this review article is to show the most promising clinical indications for the use of PET in oncology.

Positron emission tomography in cancer of the head and neck

The use of positron emission tomography (PET) has increased in oncology and in the assessment of head and neck tumours, where it is most useful for recurrent disease. It has good sensitivity and specificity for diagnosis and staging but is generally not necessary except in difficult cases. Quantitative measures of uptake on PET at diagnosis and after treatment do seem to have prognostic value independent of other information about the tumour and so PET may influence management. It also has a role in the identification of an unknown primary site and of synchronous primaries and metastases (often missed by other imaging). Fusion imaging with magnetic resonance (MRI) or computed tomography (CT) adds a new dimension with improved value for each technique.

The role of fluorodeoxyglucose positron emission tomography in cervical lymph node metastases from an unknown primary tumor

BACKGROUND

The authors performed a comprehensive review of the efficacy of fluorodeoxyglucose positron emission tomography (FDG-PET) in the detection of primary tumors in patients with cervical metastases from unknown primary tumors.

METHODS

Sixteen studies (involving a total of 302 patients) published between 1994 and 2003 were reviewed. These studies evaluated the role of FDG-PET in the detection of unknown primary tumors after conventional workup. In all studies, conventional workup included either panendoscopy or computed tomographic/magnetic resonance imaging, and in 10 of 16 studies, both of these diagnostic techniques were performed before diagnosis.

RESULTS

The overall sensitivity, specificity, and accuracy rates of FDG-PET in detecting unknown primary tumors were 88.3%, 74.9%, and 78.8%, respectively. Furthermore, FDG-PET detected 24.5% of tumors that were not apparent after conventional workup. FDG-PET imaging also led to the detection of previously unrecognized metastases in 27.1% of patients (regional, 15.9%; distant, 11.2%). FDG-PET had notably low specificity and a high false-positive rate (39.3%) in the tonsils. In contrast, the false-positive rates for FDG-PET of the base of tongue and hypopharynx were only 21.4% and 8.3%, respectively. FDG-PET exhibited decreased sensitivity to tumors in the base of tongue (81.5%). The sensitivity of this technique at other sites was 90.5%.

CONCLUSIONS

FDG-PET detected primary tumors that went undetected by other modalities in approximately 25% of cases and was sensitive in the detection of previously unrecognized regional or distant metastases in 27% of cases. FDG-PET had low specificity for tonsillar tumors and low sensitivity for base-of-tongue malignancies.

PET: a revolution in medical imaging

FDG-PET has had remarkable influence on the assessment of physiologic and pathologic states. The authors predict that FDG-PET imaging could soon become the most common procedure used by nuclear medicine laboratories and could remain so for an extended period of time. The power of molecular imaging lies in the vast potential for using biochemical and pharmacologic probes to extend applications arising from an understanding of cell biology to a large number of well-characterized pathologic states. Molecular imaging based upon tracer kinetics with positron-emitting radiopharmaceuticals could become the main source of information for the management of cancer patients. In that case, nuclear medicine procedures might become the most common imaging studies performed in the practice of medicine. This speculation is not farfetched when one realizes the enormous change that a single biologically important compound, FDG, has brought to the medical arena. The major challenge today is to attract the highly qualified individuals and to secure the resources needed to harness the opportunities in the specialty of molecular imaging.

In search of an unknown primary tumour presenting with extracervical metastases: the diagnostic performance of FDG-PET

A retrospective study was carried out to determine the performance of 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) in patients with unknown primary tumours presenting with metastases external to the neck. All patients referred to an academic PET centre (July, 1997 to December, 2000) presenting with an extracervical metastasis and no prior systemic therapy were eligible. The minimum follow-up period was 11 months. From 63 eligible cases, known metastases were FDG avid in all but one neuroendocrine process. PET scans were retrospectively classified as positive for a primary tumour (n=29), i.e. revealing at least one anatomical site suspected to be the primary tumour. This was confirmed in 16, either by histology (n=10) or radiological and clinical follow-up (n=6). There were four false positive cases. In nine patients, the primary tumour was never confirmed. Of the remaining 33 negative PET scans the primary tumour was clinically not found in 18. Follow-up and additional pathology investigations demonstrated the primary tumour in 15. A survey on clinical usefulness of PET (response rate 83%) suggested that PET positively contributed to diagnostic understanding in 29 of 52 evaluable cases. Applied late in the diagnostic trajectory, approximately four patients need to be scanned by PET in order to find one primary tumour. However, in addition to direct demonstration of unknown primaries, there appears to be a positive effect on the diagnostic work-up of these patients of a similar magnitude.

Unknown primary tumors: detection with dual-modality PET/CT--initial experience

PURPOSE

To retrospectively evaluate fused positron emission tomography (PET)/computed tomography (CT) in depicting the primary lesion in cancer of an unknown primary tumor, compared with PET, CT, and PET and CT side-by-side evaluation.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Forty-five patients (26 men and 19 women) with metastatic cervical adenopathy (n = 18) or extracervical metastases (n = 27) of unknown primary tumor were included. The mean age of the patients was 57 years (range, 29-95 years). PET/CT imaging was performed in all patients 1 hour after administration of 350 MBq of fluorodeoxyglucose with a whole-body field of view. Contrast agents were administered orally and intravenously in all patients to ensure diagnostic CT data. PET/CT data sets were evaluated for the primary tumor, and imaging results were compared with those of CT, PET, and PET and CT side-by-side evaluation. Differences in diagnostic performance were assessed by using the McNemar test with Bonferroni correction, which accounts for multiple comparisons.

RESULTS

PET/CT depicted the primary tumor in 15 (33%) of 45 patients. In 30 (67%) patients, the primary tumor site remained occult (P > .05). PET and CT side-by-side evaluation depicted 13 (29%) of 45 tumors (P > .05). PET alone revealed the primary tumor in 11 (24%) of 45 patients (P > .05), while CT alone helped in the correct diagnosis in eight (18%) of 45 patients (P > .05). There were no significant differences between the diagnostic accuracies of PET/CT and the other imaging modalities.

CONCLUSION

PET/CT was able to depict more primary tumors, though not significantly, than either of the other imaging modalities, but larger patient cohorts are required to finally judge its value for revealing the primary tumor site.

[Metastatic cutaneous adenocarcinoma of unknown primary site. Case report]

BACKGROUND

Metastases may be the first manifestation of adenocarcinoma. Up to 60% are cutaneous and present in advanced stage neoplasms. Research for the primary site is costly and requires endoscopy, imaging and immunohistochemical exams. The primary site becomes obvious in only 15% to 20% of live patients and is detected mainly at autopsy.

AIM

To report a case of metastatic cutaneous moderately differentiated adenocarcinoma of unknown primary site, located in the lower left abdomen.

RESULTS

The lesion was surgically resected. Primary site was not found by any imaging or endoscopy exams. The immunohistochemistry was negative for CEA, CK20, PSA and positive for CK7. Based on these exams, prostate and colorectal cancer were excluded. The pancreas and biliary tract were considered as the probable primary site.

CONCLUSION

The research for the primary site still is difficult, expensive and is not effective to the treatment of metastatic adenocarcinomas.

2-deoxy-fluorglucose–positron emission tomography imaging of the brain: Current clinical applications with emphasis on the dementias

A number of very significant advances in the field of positron emission tomography (PET) imaging are now beginning to have an impact on clinical PET brain imaging. Among the most significant advances are further improvements in PET scanner detectors and computers. Increasingly, more sophisticated methods of image analysis and quantitation are also beginning to emerge. In addition, there has been a very rapid introduction of newer PET radiotracers that will ultimately work their way into the clinical environment. Finally, there is an expanding interest in the potential of PET brain imaging in the evaluation of a wide variety of clinical neuropsychiatric conditions.

Cancer of unknown primary: changing approaches. A multidisciplinary case presentation from the Joan Karnell cancer center of pennsylvania hospital

Cancer of unknown primary is a common clinical syndrome, accounting for 2%-5% of cancer patients. A representative case is presented. This heterogenous group of disorders includes entities such as poorly differentiated carcinoma of unknown primary, adenocarcinoma of unknown primary, neuroendocrine carcinoma of unknown primary, squamous cell carcinoma of unknown primary, poorly differentiated (not otherwise specified) cancer of unknown primary, and melanoma of unknown primary. It is crucial to identify those treatment-responsive presentations of unknown primary with the greatest potential for long-term survival. This discussion emphasizes newer approaches to the diagnosis and treatment of unknown primary cancer, including advances in pathology with immunoperoxidase and molecular genetic techniques, positron emission tomography, and published chemotherapeutic trials. With the increased sophistication of pathologic and radiologic techniques, the frequency of unknown primary cancers will likely continue to decline. Further, as newer and more targeted therapies for specific types of cancer are identified, the previously held nihilism regarding the search for and identification of the primary may become less supportable.

Positron emission imaging of head and neck cancer, including thyroid carcinoma

Most positron emission tomography (PET) imaging studies in head and neck cancer are performed using the radiotracer 18-fluorodeoxyglucose ((18)FDG). PET with FDG has become a standard clinical imaging modality in patients with head and neck cancer. It contributes valuable information in localizing a primary tumor in patients with neck nodal metastases from an unknown primary, in the staging of primary head and neck cancer, and in the detection of recurrent disease. In addition, FDG-PET provides independent prognostic information in patients with newly diagnosed and recurrent head and neck cancer. PET/CT improves lesion localization and accuracy of FDG-PET and is strongly recommended in patients with head and neck cancer. After thyroidectomy, FDG-PET has proven useful in patients with clinical or serological evidence of recurrent or metastatic thyroid carcinoma but negative whole body iodine scan. PET shows metastatic disease in up to 90% of these patients, thereby providing a rational basis for further studies and therapy. In patients with medullary thyroid cancer with elevated calcitonin levels following thyroidectomy, FDG-PET has a sensitivity of 70-75% for localizing metastatic disease. Occasionally incidental intense FDG uptake is observed in the thyroid gland on whole body PET studies performed for other indications. Although diffuse FDG uptake usually indicates thyroiditis, focal uptake has been related to thyroid cancer in 25-50% of cases and should therefore be evaluated further if a proven malignancy would cause a change in patient management.

Carboplatin, doxorubicin and etoposide in the treatment of tumours of unknown primary site

The aim of this study was to assess the activity and toxicity of a platinum-based treatment on a group of patients with unknown primary tumours (UPTs). Patients with a diagnosis of UPT underwent a standard diagnostic procedure. Treatment was started within 2 weeks from diagnosis and consisted of carboplatin 400 mg m(-2) day 1, doxorubicin 50 mg m(-2) day 1, etoposide 100 mg m(-2) days 1-3, every 21 days. Response was evaluated after three courses and treatment continued in case of objective response (OR) or symptom control. A total of 102 patients were eligible. The median age was 59 years, sex male/female 54/48, histology was mainly adenocarcinoma or poorly differentiated carcinoma. Nodes, bone, liver and lung were the most frequently involved sites. In all, 79 patients received at least three courses of treatment; 26 patients received six courses or more. Six complete responses and 21 partial responses were observed, for a total of 27 of 102 ORs or 26.5% (95% confidence interval 18.2-36.1%). The median survival was 9 months and median progression-free survival was 4 months. Toxicity was moderate to severe, with 57.8% of patients experiencing grade III-IV haematological toxicity, mainly leucopenia. The regimen employed has shown activity in tumours of unknown primary site, but was associated with significant toxicity. Such toxicity may be considered unjustified, given the large proportion of patients with tumours not likely to respond. Efforts should therefore be addressed to identify predictors of response to chemotherapy, thus limiting aggressive treatment to those patients who could benefit from it.

Whole-body positron emission tomography using fluorodeoxyglucose in patients with metastases of unknown primary tumours (CUP syndrome)

The aim of this study was to evaluate the clinical performances of whole body 2-[18F]fluorodeoxyglucose positron emission tomography (FDG PET) imaging for the detection of the primary tumour in patients with metastases of unknown origin. Forty-one patients, without previous history of known cancer (18 women and 23 men; average age 64.1 years) with metastasis confirmed by histopathological analysis were included in a retrospective study. Results of PET were compared with those of techniques used in the current conventional diagnostic procedure. All known metastatic lesions were detected by PET. There were 26 true-positive and two false-negative results. Primary tumour remained undetermined in eight patients after conventional investigations and PET. PET was superior to conventional diagnostic procedure in 11 patients and led to modify treatment in 11 patients. Sensitivity of PET was superior than computed tomography in detecting abdominal primary tumours. FDG PET is useful in patients with unknown primary tumour because its sensitivity is good and it could modify the disease management. Otherwise, PET allows the evaluation of the extent of the disease and could be used to monitor treatment efficiency. Its contribution has to be evaluated particularly in patients with primary tumour with a specific treatment.

Diagnostic strategies for unknown primary cancer

Unknown primary cancer (UPC) is defined by the presence of metastatic disease for which a primary site is undetectable on presentation. Computed tomography scan of the body was performed routinely in search of the primary cancer and invasive procedures were pursued in selective cases. Magnetic resonance imaging of the breast enables identification of an occult breast primary tumor in < or = 75% of women who present with adenocarcinoma in the axillary lymph nodes and can influence surgical management. Positron emission tomography scan also can be used in the diagnosis of UPCs, but its value is controversial. Cytokeratins 7 and 20 and thyroid transcription factor are some of the histochemical markers used in most patients who present with metastatic adenocarcinoma. Some of the newly discovered immunohistochemical markers further assist in narrowing the differential diagnosis. The role of molecular profiling to make the diagnosis, establish the prognosis, and assess the response to treatment in UPCs is evolving. The authors discuss the role of histochemical markers in the diagnosis of UPC and the most recent data regarding the use of imaging and invasive diagnostic modalities and gene expression profiles.

Implications of PET based molecular imaging on the current and future practice of medicine

The last quarter century has witnessed the introduction of a variety of powerful techniques that have allowed visualization of organ structure and function with exquisite detail. This in turn has brought about a true revolution in the day-to-day practice of medicine. Structural imaging with x-ray computerized tomography and magnetic resonance imaging has added tremendously to many areas of medicine, including preoperative evaluation of patients. Many surgical procedures have been replaced by minimally invasive techniques, which have become a reality only because of the availability of modern imaging modalities. However, despite such accomplishments, structural imaging is quite insensitive for detecting early disease in which there often are no gross structural alterations in organ anatomy. Therefore, these modalities should be complemented by methodologies that can detect abnormalities at the molecular and cellular levels. The introduction of [(18)F]-fluorodeoxyglucose positron emission tomography (FDG-PET) in 1976 as a molecular imaging technique clearly has shown the power of this approach for treating a multitude of serious disorders. The impact of FDG-PET has been particularly impressive in patients with cancer diagnosis, for whom it has become important in staging, monitoring response to treatment, and detecting recurrence. In this review, we emphasize the role of FDG-PET in the assessment of central nervous system maladies, malignant neoplastic processes, infectious and inflammatory diseases, and cardiovascular disorders. New radiotracers are being developed and promise to expand further the list of indications for PET. These include novel tracers for cancer diagnosis and treatment capable of detecting hypoxia and angiogenesis. Prospects for developing new tracers for imaging other organ diseases also appear very promising.

Clinical applications of PET in oncology

Positron emission tomography (PET) provides metabolic information that has been documented to be useful in patient care. The properties of positron decay permit accurate imaging of the distribution of positron-emitting radiopharmaceuticals. The wide array of positron-emitting radiopharmaceuticals has been used to characterize multiple physiologic and pathologic states. PET is used for characterizing brain disorders such as Alzheimer disease and epilepsy and cardiac disorders such as coronary artery disease and myocardial viability. The neurologic and cardiac applications of PET are not covered in this review. The major utilization of PET clinically is in oncology and consists of imaging the distribution of fluorine 18 fluorodeoxyglucose (FDG). FDG, an analogue of glucose, accumulates in most tumors in a greater amount than it does in normal tissue. FDG PET is being used in diagnosis and follow-up of several malignancies, and the list of articles supporting its use continues to grow. In this review, the physics and instrumentation aspects of PET are described. Many of the clinical applications in oncology are mature and readily covered by third-party payers. Other applications are being used clinically but have not been as carefully evaluated in the literature, and these applications may not be covered by third-party payers. The developing applications of PET are included in this review.