No characteristics that are unique to CUP relative to metastases from known primaries have been identified. Abnormalities in chromosomes 1 and 12 and other complex cytogenetic abnormalities have been reported. Aneuploidy has been described in 70% of CUP patients with metastatic adenocarcinoma or undifferentiated carcinoma. The overexpression of various genes, including Ras, bcl-2 (40%), her-2 (11%), and p53 (26–53%), has been studied in CUP samples, but they have no effect on response to therapy or survival. The extent of angiogenesis in CUP relative to that in metastases from known primaries has also been evaluated, but no consistent findings have emerged.
Obtaining a thorough medical history from CUP patients is essential, paying particular attention to previous surgeries, removed lesions, and family medical history to assess potential hereditary cancers. Physical examination, including a digital rectal examination in men and breast and pelvic examinations in women, should be performed. Determining the patient's performance status, nutritional status, comorbid illnesses, and cancer-induced complications is essential since these may affect treatment planning.
Role of Serum Tumor Markers and Cytogenetics
Most tumor markers, including CEA, CA-125, CA 19-9, and CA 15-3, when elevated, are nonspecific and not helpful in determining the primary tumor site. Men who present with adenocarcinoma and osteoblastic metastasis should undergo a prostate-specific antigen (PSA) test. In patients with undifferentiated or poorly differentiated carcinoma (especially with a midline tumor), elevated β-human chorionic gonadotropin (βhCG) and α fetoprotein (AFP) levels suggest the possibility of an extragonadal germ cell (testicular) tumor. Cytogenetic studies had a larger role in the past, although interpretation of these older studies can be challenging. In our opinion, with the availability of immunohistochemical stains, cytogenetic analyses are indicated only occasionally. We reserve them for undifferentiated neoplasms with inconclusive immunohistochemical stains and those for which a high suspicion of lymphoma exists.
Chest x-rays are always obtained in CUP workups but are often negative, especially with low-volume disease. A CT scan of the chest, abdomen, and pelvis is indicated in the search for the primary, evaluate the extent of disease, and select the most favorable biopsy site. Older studies suggested that the primary tumor site is detected in 20–35% of patients who undergo a CT scan of the abdomen and pelvis, although by current definition these patients would not be considered as having CUP. Older studies also suggest a latent primary tumor prevalence of 20%; with more sophisticated imaging, this prevalence is <5% today.
Mammography should be performed in all women who present with metastatic adenocarcinoma, especially in those with adenocarcinoma and isolated axillary lymphadenopathy. MRI of the breast is a recognized follow-up modality in patients with suspected occult primary breast carcinoma following a negative mammography and sonography. The results of these imaging modalities can influence surgical management; a negative breast MRI result predicts a low tumor yield at mastectomy.
A conventional workup for a squamous cell carcinoma and cervical CUP (neck lymphadenopathy with no known primary tumor) includes a CT scan or MRI and invasive studies, including indirect and direct laryngoscopy, bronchoscopy, and upper endoscopy. Ipsilateral (or bilateral) tonsillectomy (with histopathology) has been recommended for these patients. Fluorodeoxyglucose positron emission tomography (FDG-PET) scans are useful in this patient population and may help guide the biopsy; determine the extent of disease; facilitate the appropriate treatment, including planning radiation fields; and help with disease surveillance. A smaller radiation field encompassing the primary (when found) and metastatic adenopathy decreases the risk of chronic xerostomia. Several studies have evaluated the utility of PET in patients with cervical CUP. These trials have included a small number of patients; primary tumors were identified in ∼21–30%.
The diagnostic contribution of PET to the evaluation of other CUP (outside of the neck adenopathy indication) is controversial. PET-CT can be helpful for patients who are candidates for surgical intervention for solitary metastatic disease because the presence of disease outside the primary site may affect surgical planning.
Invasive studies, including upper endoscopy, colonoscopy, and bronchoscopy, should be limited to symptomatic patients or those with laboratory, imaging or pathologic abnormalities that suggest that these techniques will result in a high yield in search for a primary cancer.
Pathologic Diagnosis of CUP
A detailed pathologic examination of the most accessible biopsied tissue specimen is mandatory in CUP patients. Pathologic evaluation typically consists of hematoxylin-and-eosin stains and immunohistochemical tests. Electron microscopy and cytogenetics are rarely useful.
Light Microscopy Evaluation
Adequate tissue obtained by fine-needle aspiration or core-needle biopsy should first be stained with hematoxylin and eosin and subjected to light microscopic examination. On light microscopy, 60–65% of CUP are adenocarcinoma, and 5% are squamous cell carcinoma. The remaining 30–35% are poorly differentiated adenocarcinoma, poorly differentiated carcinoma, poorly differentiated neoplasm. A small percentage of lesions are diagnosed as neuroendocrine cancers (2%), mixed tumors (adenosquamous, or sarcomatoid carcinomas), or undifferentiated neoplasms (Table 99–1).
Table 99–1 Major Histologies in Cup |Favorite Table|Download (.pdf)
Table 99–1 Major Histologies in Cup
|Well to moderately differentiated adenocarcinoma||60|
|Squamous cell cancer||5|
|Poorly differentiated adenocarcinoma, poorly differentiated carcinoma||30|
Role of Immunohistochemical Analysis
Immunohistochemical stains are peroxidase-labeled antibodies against specific tumor antigens that are used to define tumor lineage. The number of available immunohistochemical stains is ever-increasing. However, in CUP cases, more is not necessarily better, and immunohistochemical stains should be used in conjunction with the patient's clinical presentation and imaging studies to select the best therapy. Communication between the clinician and pathologist is essential. No stain is 100% specific, and overinterpretation should be avoided. PSA and thyroglobulin tissue markers, which are positive in prostate and thyroid cancer, respectively, are the most specific of the current marker panel. However, these cancers rarely present as CUP, so the yield of these tests may be low. Fig. 99-1 delineates a simple algorithm for immunohistochemical staining in CUP cases. Table 99–2 lists additional tests that may be useful to further define the tumor lineage. A more comprehensive algorithm may improve the diagnostic accuracy but can make the process complex. With the use of immunohistochemical markers, electron microscopic analysis, which is time-consuming and expensive, is rarely needed.
Approach to cytokeratin (CK7 and CK20) markers used in CUP.
Table 99–2 Additional Immunohistochemical Stains Useful in the Diagnosis of CUP |Favorite Table|Download (.pdf)
Table 99–2 Additional Immunohistochemical Stains Useful in the Diagnosis of CUP
|Estrogen and progesterone receptors||Breast cancer|
|Gross cystic disease fibrous protein-15||Breast cancer|
|Thyroid transcription factor 1||Lung and thyroid cancer|
|Chromogranin, synaptophysin, CD56||Neuroendocrine cancer|
|Leukocyte common antigen||Lymphoma|
|HMB-45, tyrosinase, Melan-A||Melanoma|
|URO-III, thrombomodulin||Bladder cancer|
|α Fetoprotein||Hepatocellular cancer, germ cell cancer|
|β-Human chronic gonadotropin||Germ cell cancer|
|Prostate specific antigen||Prostate cancer|
|WT-1, estrogen receptor (ER)||Müllerian/ovarian cancer|
|RCC, CD 10||Renal cell carcinoma|
There are >20 subtypes of cytokeratin (CK) intermediate filaments with different molecular weights and differential expression in various cell types and cancers. Monoclonal antibodies to specific CK subtypes have been used to help classify tumors according to their site of origin; commonly used CK stains in CUP are CK7 and CK20. CK7 is found in tumors of the lung, ovary, endometrium, and breast and not in those of the lower gastrointestinal tract, whereas CK20 is normally expressed in the gastrointestinal epithelium, urothelium, and Merkel cells. CK20+/CK7− strongly suggests a primary tumor of the colon; 75–95% of colon tumors show this pattern of staining. CK20−/CK7+ suggests cancer of the lung, breast, ovary, endometrium, and pancreaticobiliary tract; some of these can also be CK20+. The nuclear CDX-2 transcription factor, which is the product of a homeobox gene necessary for intestinal organogenesis, is often used to aid in the diagnosis of gastrointestinal adenocarcinomas.
Thyroid transcription factor 1 (TTF-1) is a 38-kDa homeodomain-containing nuclear protein that plays a role in transcriptional activation during embryogenesis in the thyroid, diencephalon, and respiratory epithelium. TTF-1 nuclear staining is typically positive in lung and thyroid cancers. Approximately 68% of adenocarcinomas and 25% of squamous cell lung cancers stain positive for TTF-1, which helps differentiate a lung primary tumor from metastatic adenocarcinoma in a pleural effusion, the mediastinum, or the lung parenchyma.
Distinguishing pleural mesothelioma from lung adenocarcinoma can be challenging. Calretinin, Wilms' tumor gene-1 (WT-1), and mesothelin have been suggested as useful markers for mesothelioma. Gross cystic disease fibrous protein-15, a 15-kDa monomer protein, is a marker of apocrine differentiation that is detected in 62–72% of breast carcinomas. UROIII, high-molecular-weight cytokeratin, thrombomodulin, and CK20 are the markers used to diagnose lesions of urothelial origin.
Role of DNA Microarray and Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) in CUP
In the absence of a known primary, developing therapeutic strategies for CUP is challenging. The current diagnostic yield with imaging and immunochemistry is ∼20–30% for CUP patients. The use of gene expression studies holds the promise of substantially increasing this yield. Gene expression profiles are most commonly generated using quantitative RT-PCR or DNA microarray.
Neural network programs have been used to develop predictive algorithms from the gene expression profiles. Typically, a training set of gene profiles from known cancers (preferably from metastatic sites) are used to train the software. The program can then be used to predict the putative origin of a test tumor, and presumably of true CUP. Comprehensive gene expression databases that have become available for common malignancies may also be useful in CUP. Investigators have used expression data from normal differentiated tissues to identify conserved expression profiles found in malignant tissue as a basis for predicting the tissue of origin (ToO). These approaches have been effective in blind testing against known primary cancers and their metastasis. However, because, by definition, the primary tumor site is not identifiable in CUP, validation of site prediction in this setting can be challenging, and any predictions currently must be supported by clinical and pathologic correlation. Prospective validation trials are currently evaluating the role of molecular studies identifying ToO in CUP and its impact on management. Early trials suggest that the profiling approach is feasible from archived formalin-fixed paraffin-embedded (FFPE) core-needle biopsies. Quantitative RT-PCR on fine-needle aspiration samples is very useful in clinical practice. Data from some studies suggest that a putative primary profile can be applied to 80–85% of cases. At present, the best confirmation of molecular profiling studies in CUP is an indirect validation based on the patient's presentation and clinical course. Current studies are geared to understanding profiling tools' accuracy, clinical effectiveness, and how these assays complement immunohistochemistry and help guide therapy.
Treatment: Carcinoma of Unknown Primary
The treatment of CUP continues to evolve, albeit slowly. The median survival duration of most patients with disseminated CUP is ∼6–10 months. Systemic chemotherapy is the primary treatment modality in most cases, but the careful integration of surgery, radiation therapy, and even periods of observation are important in the overall management of this condition (Figs. 99-2 and 99-3). Prognostic factors include performance status, site and number of metastases, response to chemotherapy, and serum lactate dehydrogenase (LDH) levels. Culine and colleagues developed a prognostic model using performance status and serum LDH levels, which allowed the assignment of patients into two subgroups with divergent outcomes. Future prospective trials using this prognostic model are warranted. Clinically, several CUP diagnoses fall into a favorable prognostic subset. Others, including those with disseminated CUP that do not fit a subset, have a more unfavorable prognosis.
Treatment algorithm for adenocarcinoma and poorly differentiated adenocarcinoma CUP. C, chemotherapy; CRT, chemoradiation; GI, gastrointestinal; IHC, immunohistochemistry; MRI, magnetic resonance imaging; PSA, prostate-specific antigen; RT, radiation.
Treatment algorithm for squamous cell CUP. C, chemotherapy; CT, computed tomography; PET, positron emission tomography; RT, radiation.
Treatment of Favorable Subsets of CUP
Women with Isolated Axillary Adenopathy
Women with isolated axillary adenopathy with adenocarcinoma or carcinoma are usually treated for stage II or III breast cancer based on pathologic findings. These patients should undergo a breast MRI if mammogram and ultrasound are negative. Radiation therapy to the ipsilateral breast is indicated if the breast MRI is positive. Chemotherapy and/or hormonal therapy is indicated based on patient's age (premenopausal or postmenopausal), nodal disease bulk, and hormone receptor status (Chap. 90). It is important to verify that the pathology does represent a breast cancer profile (morphology, immunohistochemical markers including HER-2, gene expression) before embarking on a breast cancer therapeutic program.
Women with Peritoneal Carcinomatosis
The term primary peritoneal papillary serous carcinoma (PPSC) has been used to describe CUP with carcinomatosis with the pathologic and laboratory (elevated CA-125 antigen) characteristics of ovarian cancer but no ovarian primary tumor identified on transvaginal sonography or laparotomy. Studies suggest that ovarian cancer and PPSC, which are both of müllerian origin, have similar gene expression profiles. Similar to patients with ovarian cancer, patients with PPSC are candidates for cytoreductive surgery, followed by adjuvant taxane and platinum-based chemotherapy. In one retrospective study of 258 women with peritoneal carcinomatosis who had undergone cytoreductive surgery and chemotherapy, 22% of patients had a complete response to chemotherapy; the median survival duration was 18 months (range 11–24 months). However, not all peritoneal carcinomatosis in women is PPSC. Careful pathologic evaluation can help diagnose a colon cancer profile (CDX-2+, CK-20+, CK7−) or a pancreaticobiliary cancer.
Poorly Differentiated Carcinoma with Midline Adenopathy
Men with poorly differentiated or undifferentiated carcinoma that presents as a midline adenopathy should be evaluated for extragonadal germ cell malignancy. If diagnosed and treated as such, they often experience a good response to treatment with platinum-based combination chemotherapy. Response rates of >50% have been noted, and 10–15% long-term survivors have been reported. Older patients (especially smokers) who present with mediastinal adenopathy are more likely to have a lung or head—and-neck cancer profile.
Low-grade neuroendocrine carcinoma often has an indolent course, and treatment decisions are based on symptoms and tumor bulk. Urine 5-HIAA and serum chromogranin may be elevated and can be followed as markers. Often the patient is treated with somatostatin analogues alone for hormone-related symptoms (diarrhea, flushing, nausea). Specific local therapies or systemic therapy would only be indicated if the patient is symptomatic with local pain secondary to significant growth of the metastasis or the hormone-related symptoms are not controlled with endocrine therapy. Patients with high-grade neuroendocrine carcinoma are treated as having small cell lung cancer and are responsive to chemotherapy; 20–25% show a complete response, and up to 10% patients survive more than 5 years.
Squamous Cell Carcinoma Presenting as Neck Adenopathy
Patients with early-stage squamous cell carcinoma involving the cervical lymph nodes are candidates for node dissection and radiation therapy, which can result in long-term survival. The role of chemotherapy in these patients is undefined, although chemoradiation therapy or induction chemotherapy is often used and is beneficial in bulky N2/N3 lymph node disease.
Patients with solitary metastases can also experience good treatment outcomes. Some patients who present with locoregional disease are candidates for aggressive trimodality management; both prolonged disease-free interval and occasionally cure are possible.
Men with Blastic Skeletal Metastases and Elevated PSA
Blastic bone-only metastasis is a rare presentation, and elevated serum PSA or tumor staining with PSA may provide confirmatory evidence of prostate cancer in these patients. Those with elevated levels are candidates for hormonal therapy for prostate cancer, although it is important to rule out other primary tumors (lung most common).
Management of Disseminated CUP
Patients who present with liver, brain, and adrenal metastatic disease usually have a poor prognosis. Beside primary peritoneal carcinoma, carcinomatosis presenting as CUP in other settings is not uncommon. Gastric, appendicular, colon, pancreas, and cholangiocarcinoma are all possible primaries, and imaging, endoscopy, and pathologic data help in the evaluation.
Traditionally, platinum-based combination chemotherapy regimens have been used to treat patients with CUP. In a phase II study by Hainsworth and colleagues, 55 mostly chemotherapy-naive patients were treated with paclitaxel, carboplatin, and oral etoposide every 3 weeks. The overall response rate was 47%, with median overall survival duration of 13.4 months. Briasoulis and colleagues reported similar response rates and survival durations in 77 patients with CUP, who had been treated with paclitaxel and carboplatin. In this study, patients with nodal or pleural disease and women with peritoneal carcinomatosis had higher response rates and overall survival durations of 13 and 15 months, respectively. Studies incorporating newer agents, including gemcitabine, irinotecan, and targeted agents, are showing higher response rates. In a phase II randomized trial by Culine and colleagues, 80 patients were randomly assigned to receive gemcitabine with cisplatin or irinotecan with cisplatin; 78 patients were assessable for efficacy and toxicity. Objective responses were observed in 21 patients (55%) in the gemcitabine and cisplatin arm and in 15 patients (38%) in the irinotecan and cisplatin arm. The median survival was 8 months for gemcitabine and cisplatin and 6 months for irinotecan and cisplatin.
The role of second-line chemotherapy in CUP is poorly defined. Gemcitabine as a single agent has shown a partial response rate of 8%, and 25% of patients had minor responses or stable disease, with improved symptoms. Combination chemotherapy as a second- and third-line treatment may result in a slightly improved response and therapy options should be guided by pathology and the patient's performance status.
Hainsworth and colleagues studied the combination of bevacizumab and erlotinib in 51 patients; 25% were chemotherapy-naive and had advanced bone or liver metastases, while the rest had been treated with 1 or 2 chemotherapy regimens. Responses were noted in 4 patients (8%), and 30 patients (59%) experienced stable disease or a minor response. The median overall survival was 8.9 months, with 42% of patients alive at 1 year.
Historically, patients with CUP have been treated with broad spectrum regimens that work for a variety of primary cancers; a "one treatment fits all" approach. With incremental improved responses over the past decade in known cancer types, we anticipate overall better response rates with newer regimens for selected CUP patients. With a more robust immunohistochemical panel (directed approach) and new molecular profiling tools, one may hope to create a more tailored treatment algorithm for CUP patients.