Studies looking for unique signature abnormalities in CUP tumors have not been positive. 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. Using the Sequenom (SQM) Massarray platform, a study in consecutive CUP patients showed that the overall mutational rate was surprisingly low (18%). No “new” low-frequency mutations were found using a panel of mutations involving the P13K/AKT pathway, MEK pathway, receptors, and downstream effectors. Nevertheless, it is possible that newer “deep sequencing” techniques in select patients may yield consistent abnormalities.
Initial CUP evaluation has two goals: search for the primary tumor based on pathologic evaluation of the metastases and determine the extent of disease. Obtaining a thorough medical history from CUP patients is essential, including paying particular attention to previous surgeries, removed lesions, and family medical history to assess potential hereditary cancers. Adequate physical examination, including a digital rectal examination in men and breast and pelvic examinations in women, should be performed based on clinical presentation.
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 (β-hCG) and α fetoprotein (AFP) levels suggest the possibility of an extragonadal germ cell (testicular) tumor. With the availability of IHC, cytogenetic studies are rarely needed.
In the absence of contraindications, a baseline IV contrast computed tomography (CT) scan of the chest, abdomen, and pelvis is the standard of care. This helps to search for the primary tumor, evaluate the extent of disease, and select the most accessible 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 do not have CUP. These studies also suggest a latent primary tumor prevalence of 20%; with more sophisticated imaging, this has decreased to ≤5% today.
Mammography should be performed in all women who present with metastatic adenocarcinoma, especially in those with adenocarcinoma and isolated axillary lymphadenopathy. Magnetic resonance imaging (MRI) of the breast is a follow-up modality in patients with axillary adenopathy and suspected occult primary breast carcinoma following a negative mammography and ultrasound. 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) staging tonsillectomy has been recommended for these patients. 18-Fluorodeoxyglucose positron emission tomography (18-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 squamous cervical CUP, and head and neck primary tumors were identified in ~21–30%.
The diagnostic contribution of PET to the evaluation of other CUP (outside of the neck adenopathy indication) remains controversial and is not routinely recommended. 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 finding a primary cancer.
Role of Pathologic Studies
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.
LIGHT MICROSCOPY EVALUATION
Adequate tissue obtained preferably by excisional biopsy or core-needle biopsy (instead of only a fine-needle aspiration) is stained with hematoxylin and eosin and subjected to light microscopic examination. On light microscopy, 60–65% of CUP is adenocarcinoma, and 5% is squamous cell carcinoma. The remaining 30–35% is poorly differentiated adenocarcinoma, poorly differentiated carcinoma, or poorly differentiated neoplasm. A small percentage of lesions are diagnosed as neuroendocrine cancers (2%), mixed tumors (adenosquamous or sarcomatoid carcinomas), or undifferentiated neoplasms (Table 120e-1).
TABLE 120e-1Major Histologies in Carcinoma of Unknown Primary ||Download (.pdf) TABLE 120e-1Major Histologies in Carcinoma of Unknown Primary
|Histology ||Proportion, % |
|Well to moderately differentiated adenocarcinoma ||60 |
|Squamous cell cancer ||5 |
|Poorly differentiated adenocarcinoma, poorly differentiated carcinoma ||30 |
|Neuroendocrine ||2 |
|Undifferentiated malignancy ||3 |
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. 120e-1 delineates a simple algorithm for immunohistochemical staining in CUP cases. Table 120e-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 adenocarcinoma of unknown primary.
TABLE 120e-2Select Immunohistochemical Stains Useful in the Diagnosis of Carcinoma of Unknown Primary (CUP) ||Download (.pdf) TABLE 120e-2Select Immunohistochemical Stains Useful in the Diagnosis of Carcinoma of Unknown Primary (CUP)
|Likely Primary Profile ||Commonly Considered IHC to Assist in Differential Diagnosis of CUPa |
|Breast ||Estrogen receptor (ER), gross cystic disease fibrous protein-15 (GCDFP-15), mammaglobin, Her-2/neu |
|Ovarian/mullerian ||Estrogen receptor (ER), Wilms’ tumor gene (WT-1), CK7, PAX8, PAX2 |
|Lung adenocarcinoma ||Thyroid transcription factor (TTF-1; nuclear staining), napsin A, surfactant protein A precursor (SP-A1) |
|Germ cell ||β-hCG, AFP, OCT3/4, CKIT, CD30 (embryonal), SALL4 |
|Prostate ||PSA, α-methylacyl CoA racemase/P504S (AMACR/P504S), P501S (prostein), and prostate-specific membrane antigen (PSMA) |
|Intestinal ||CK7, CK20, CDX-2, carcinoembryonic antigen (CEA) |
|Neuroendocrine ||Chromogranin, synaptophysin, CD56 |
|Sarcoma ||Desmin (desmoid tumors), factor VIII (angiosarcomas), CD31, smooth muscle actin (leiomyosarcoma), MyoD1 (rhabdomyosarcoma) |
|Renal ||RCC, CD10, PAX8 |
|Hepatocellular carcinoma ||Hep par-1, arginase-1 (Arg-1), TTF-1 (granular cytoplasmic staining) |
|Melanoma ||S100, vimentin, HMB-45, tyrosinase and melan-A |
|Urothelial ||CK7, CK20, thrombomodulin |
|Mesothelioma ||Calretinin, WT-1 |
|Lymphoma ||Leukocyte common antigen (LCA), CD3, CD4, CD5, CD20, CD45 |
|Squamous cell carcinoma (SCC) ||p63, p40 (lung SCC), CK5/6 |
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 adenocarcinoma CUP are CK7 and CK20. CK7 is found in tumors of the lung, ovary, endometrium, breast, and upper gastrointestinal tract including pancreaticobiliary cancers, whereas CK20 is normally expressed in the gastrointestinal epithelium, urothelium, and Merkel cells. 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) 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.
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.
IHC performs the best when used in groups that give rise to patterns that are strongly indicative of certain profiles. For example, the TTF-1/CK7+ and CK20+/CDX-2+/CK7– phenotypes have been reported as very suggestive of lung and lower gastrointestinal cancer profiles, respectively, although these patterns have not been validated prospectively in the absence of a primary cancer. IHC is not without its limitations; several factors affect tissue antigenicity (antigen retrieval, specimen processing, and fixation), interpretation of stains in tumor (nuclear, cytoplasmic, membrane) versus normal tissue, inter- and intraobserver variability, and tissue heterogeneity and inadequacy (given small biopsy sizes). Communication with the pathologist is critical to determine if additional tissue will be beneficial in the pathologic evaluation.
ROLE OF TISSUE OF ORIGIN MOLECULAR PROFILING
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 reverse transcriptase polymerase chain reaction (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) is 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. These approaches have been effective in testing against known primary cancers and their metastases.
mRNA- or microRNA-based tissue of origin molecular profiling assays have been studied in prospective and retrospective CUP trials. Most of the CUP studies have evaluated assay performance, although the challenge with validating the accuracy of an assay for CUP is that, by definition, the primary cancer diagnosis cannot be verified. Thus, current estimates of tissue of origin test accuracy have relied on indirect metrics including comparison with IHC, clinical presentation, and appearance of latent primaries. Using these measures, the assays suggest a plausible primary in ~70% of patients studied. The only outcomes-based study is a single-arm study reporting a median survival of 12.5 months for patients who received assay-directed site-specific therapy. Firm conclusions of therapeutic impact cannot be drawn from this study given the nonrandomized design, statistical biases, confounding variables including use of subsequent lines of (empiric) therapy, and the heterogeneity of the CUP cancers. Additional studies are needed to better understand the clinical influence of tissue of origin profiling tools and how these assays complement IHC and help guide therapy.
TREATMENT Carcinoma of Unknown Primary GENERAL CONSIDERATIONS
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 patients with disseminated disease, but the careful integration of surgery, radiation therapy, and even periods of observation is important in the overall management of this condition (Figs. 120e-2 and 120e-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, some CUP diagnoses fall into a favorable prognostic subset. Others, including those with disseminated CUP, do not and have a more unfavorable prognosis. TREATMENT OF FAVORABLE CUP SUBSETS 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 are indicated based on patient’s age (premenopausal or postmenopausal), nodal disease bulk, and hormone receptor status (Chap. 108). It is important to verify that the pathology suggests a breast cancer profile (morphology, immunohistochemical breast markers including estrogen receptor, mammoglobin, GCDFP-15, 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 or even a mislabeled peritoneal mesothelioma (calretinin positive). 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 long-term survival rates of 10–15% long 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. Neuroendocrine carcinoma
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. Solitary metastatic site
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. Patients with nonserous papillary primary peritoneal carcinomatosis can have a large differential diagnosis, which is mainly of gastrointestinal profile and includes gastric, appendiceal, colon, and pancreaticobiliary profiles.
Traditionally, platinum-based combination chemotherapy regimens have been used to treat CUP. Several broadly used regimens have been studied in the last two decades; these include paclitaxel-carboplatin, gemcitabine-cisplatin, gemcitabine-oxaliplatin, and irinotecan and fluoropyrimidine-based therapies. These chemotherapeutic agents used as empiric regimens have shown a response rate of 25–40%, and their use obtains median survival times of 6–13 months.
Outside of favorable subsets, there is a small group of patients with a “definitive” IHC. These patients usually have a single diagnosis based on their clinicopathologic presentation and are often treated for the putative primary tumor. This does not guarantee a response, although it increases the probability of response when select drugs are chosen from a class of drugs known to work in that cancer type. Patients who do not fall into those categories are candidates for broad-spectrum platinum-based regimens, clinical trials, and additional trial-based genomic and proteomic tests. Today, we do not have effective drugs for several CUP cancer profiles, and treatments overlap for some cancers. However, as novel therapies are developed for additional known cancers, tissue of origin and assessment of molecular features of the tumor will be important and might direct more selective treatment.
Treatment algorithm for adenocarcinoma and poorly differentiated adenocarcinoma of unknown primary (CUP). C, chemotherapy; CRT, chemoradiation; GI, gastrointestinal; IHC, immunohistochemistry; MRI, magnetic resonance imaging; PSA, prostate-specific antigen; RT, radiation.
Treatment algorithm for squamous cell carcinoma of unknown primary (CUP). C, chemotherapy; CT, computed tomography; PET, positron emission tomography; RT, radiation.