Utility of immunohistochemistry in separating thymic neoplasms from germ cell tumors and metastatic lung cancer involving the anterior mediastinum

Utility of Immunohistochemistry in the Diagnosis of Pleuropulmonary and Mediastinal Cancers: A Review and Update

CONTEXT.—

Immunohistochemistry has become a valuable ancillary tool for the accurate classification of pleuropulmonary and mediastinal neoplasms necessary for therapeutic decisions and predicting prognostic outcome. Diagnostic accuracy has significantly improved because of the continuous discoveries of tumor-associated biomarkers and the development of effective immunohistochemical panels.

OBJECTIVE.—

To increase the accuracy of diagnosis and classify pleuropulmonary neoplasms through immunohistochemistry.

DATA SOURCES.—

Literature review and the author's research data and personal practice experience.

CONCLUSIONS.—

This review article highlights that appropriately selecting immunohistochemical panels enables pathologists to effectively diagnose most primary pleuropulmonary neoplasms and differentiate primary lung tumors from a variety of metastatic tumors to the lung. Knowing the utilities and pitfalls of each tumor-associated biomarker is essential to avoid potential diagnostic errors.

Pattern of placental alkaline phosphatase (PLAP) expression in human tumors: a tissue microarray study on 12,381 tumors

Placental alkaline phosphatase (PLAP) is commonly expressed at high levels in testicular germ cell tumors. PLAP immunohistochemistry (IHC) is thus often used to confirm this diagnosis, especially in cases of putative metastasis. However, other tumors can also express PLAP. To comprehensively determine PLAP expression in normal and tumor tissue, a tissue microarray containing 16,166 samples from 131 different tumor types and subtypes as well as 608 samples from 76 different normal tissue types was analyzed by IHC. Moderate to strong PLAP positivity was found in 27 (21%) of 131 different tumor types including seminoma (96%), embryonal carcinoma (85%), and yolk sac tumors of the testis (56%); endometrioid carcinoma of the endometrium (28%) and the ovary (20%); gastric adenocarcinoma (22%); serous carcinoma (not otherwise specified) of the ovary (17%) and the uterus (11%); adenocarcinoma of the ampulla of Vater (15%); carcinosarcoma of the ovary (11%) and the uterus (8%); esophageal adenocarcinoma (10%); invasive urothelial carcinoma (4%); cholangiocarcinoma (2%); and adenocarcinoma of the lung (1%). Low‐level PLAP immunostaining, often involving only a small fraction of tumor cells, was seen in 21 additional tumor entities. The clinical significance of PLAP expression may vary between tumor types as high PLAP expression was linked to advanced pathological tumor stage (p = 0.0086), nodal metastasis (p = 0.0085), and lymphatic (p = 0.0007) and blood vessel invasion (p = 0.0222) in colorectal cancer, but to low pathological tumor stage in endometrial cancer (p = 0.0043). In conclusion, our data identify several tumor entities that can show PLAP expression at comparable levels to testicular germ cell tumors. These tumor entities need to be considered in cases of PLAP‐positive metastasis. Low‐level PLAP expression can be found in various other tumor entities and should generally not be viewed as a strong argument for germ cell neoplasia.

Primary Thymic Signet Ring Cell Adenocarcinoma: A Currently Unrecognized Variant

We describe the first case of primary thymic adenocarcinoma with signet ring cell features. The patient was a 39-year-old Filipino male who presented with a huge anterior mediastinal mass extending to the left supraclavicular fossa, which underwent an incisional biopsy. Extensive clinicoradiological work-up showed no evidence of any primary tumor in other organs, and radiological imaging confirmed a primary tumor location in the thymic area. He later developed bilateral pleural and pericardial effusions and eventually died of his tumor. The biopsy contained a neoplastic growth of solid nests made of cells with prominent signet ring features in sclerotic stroma. Immunohistochemically, the tumor cells were reactive for cytokeratin 7, carcinoembryonic antigen, and CD5 and negative for cytokeratin 20, TTF1, napsin A, α-fetoprotein, PAX-8, CD-117, CA19-9, CA-125, CDX2, p63, and CD99. No genetic alterations of ALK, RET, and ROS1 were found, nor was any ALK or ROS1 immunostaining detected, as known to occur in a fraction of primary pulmonary adenocarcinomas. Morphologically, this thymic tumor resembled signet ring cell adenocarcinomas of other locations, including, stomach, pancreas, and lung, but CD5 immunoreactivity strongly supported the clinical and radiological evidence of a primary thymic origin. In the English literature, only 58 cases of primary thymic adenocarcinoma are on record and this is the first report of a signet ring cell variant, which further broadens the morphological spectrum of thymic adenocarcinoma subtypes.

Differential diagnostic value of CD5 and CD117 expression in thoracic tumors: a large scale study of 1465 non-small cell lung cancer cases

Background

Thoracic pathologists are frequently faced with tissue specimens from intrathoracic/mediastinal tumors. Specifically the differentiation between thymic and pulmonary squamous cell carcinomas (SqCC) can be challenging. In order to clarify the differential diagnostic value of CD5 and CD117 in this setting, we performed a large scale expression study of both markers in 1465 non-small cell lung cancer (NSCLC) cases.

Methods

Tissue microarrays of formalin-fixed paraffin-embedded resection specimens of 1465 NSCLC were stained with antibodies against CD117 and CD5. Positivity of both markers was correlated with clinicopathological variables.

Results

CD117 was positive in 145 out of 1457 evaluable cases (9.9 %) and CD5 was positive in 133 out of 1427 evaluable cases (9.3 %). 28 cases (1.9 %) showed coexpression of CD117 and CD5. Among the 145 cases that were positive for CD117, 97 (66.8 %) were adenocarcinomas (ADC), 34 (23.4 %) were SqCC, 5 (3.4 %) were adenosquamous carcinomas (ADSqCC), 8 (5.5 %) were large cell carcinomas (LC), and one (0.6 %) was a pleomorphic carcinoma (PC). In the CD5 positive group consisting of 133 cases, 123 (92.4 %) were ADC, 0 (0 %) were SqCC, 4 (3.0 %) were ADSqCC, 3 (2.2 %) LC and 3 (2.2 %) were PC. None of the 586 SqCC showed expression of CD5. No association of CD117- or CD5 positivity to patients’ age, pathological stages or to T-, N-, or M- categories was observed.

Conclusions

A substantial subset of NSCLC exhibit positivity of CD117 and CD5. Since CD5 expression was not observed in pulmonary SqCC, but is expressed in the majority of thymic squamous cell carcinomas, the application of this immunomarker is a valuable tool in the differential diagnosis of thoracic neoplasms.

Electronic supplementary material

The online version of this article (doi:10.1186/s13000-015-0441-7) contains supplementary material, which is available to authorized users.

Immunohistochemistry in the diagnosis of thymic epithelial neoplasms

The diagnosis of thymic epithelial neoplasms is normally rendered after careful evaluation of their histologic features. In some cases, however, the morphological heterogeneity or overlap with neoplasms of other organ systems can lead to diagnostic uncertainty. On the basis of this, the use of immunohistochemical stains as a diagnostic adjunct has become a popular tool. Although undoubtedly, immunohistochemistry has its role in the diagnosis of difficult cases, to date there are no specific markers that would distinguish thymic epithelial neoplasms from other tumors and interpretation of immunohistochemical results should only ever be made in conjunction with accurate morphologic analysis and careful clinical evaluation. This article will review the current knowledge of the immunohistochemical phenotype of thymic epithelial neoplasms with particular emphasis on its use for diagnostic purposes and the latest advances in this field.

Thymic carcinoma, part 1: a clinicopathologic and immunohistochemical study of 65 cases

The clinicopathologic and immunohistochemical features of 65 primary thymic carcinomas are reported (43 men and 22 women; 19-81 years old). Thymectomy was performed in all cases. Masaoka staging for 53 patients showed 3 patients in stage I, 14 in stage II, 17 in stage III, and 19 in stage IV. Histologic studies revealed 9 carcinoma subtypes. Immunohistochemically, the tumors showed high rates of expression for cytokeratin, Pax8, and FoxN1. Follow-up for 62 patients revealed that 36 patients were alive (mean follow-up, 51.1 months) and 26 had died (mean survival, 47.5 months). The 3- and 5-year overall survival rates were 76.6% and 65.7%, respectively. Our findings suggest that thymic carcinomas may behave less aggressively than commonly believed. Lymph node status and tumor size seem to be important prognostic factors. The Masaoka staging system does not seem to reliably predict outcome.

SALL4 is a novel sensitive and specific marker for metastatic germ cell tumors, with particular utility in detection of metastatic yolk sac tumors

BACKGROUND

The correct diagnosis of metastatic germ cell tumors is critical, because these tumors can be effectively treated and are even cured with modern therapy. Their histopathologic diagnosis can be challenging without immunohistochemical markers, which currently have limitations. SALL4 is a novel stem cell marker essential to maintain pluripotency and self-renewal of embryonic stem cells. In the current study, the authors investigated the utility of SALL4 as a potential diagnostic marker for metastatic germ cell tumors.

METHODS

Ninety metastatic germ cell tumors from testis, ovary, and extragonadal sites were stained with a monoclonal SALL4 antibody. In addition, 170 metastatic nongerm cell malignancies, including 158 carcinomas (6 head and neck, 8 thyroid, 12 lung, 8 breast, 7 hepatocellular, 3 cholangiocarcinomas, 2 ampullary, 10 pancreatic, 18 gastric, 15 esophageal, 10 renal cell, 10 urothelial, 12 prostatic, 18 ovarian, 6 uterine, and 13 colonic) and 12 melanomas, were also stained to test SALL4 specificity.

RESULTS

All 22 seminomas, 7 dysgerminomas, 22 embryonal carcinomas, and 14 of 15 yolk sac tumors displayed strong and diffuse SALL positivity in >90% of tumor cells (80% of tumor cells were strongly positive in the remaining yolk sac tumor). Five of 7 choriocarcinomas and 9 of 18 teratomas were also variably positive for SALL4. In contrast, only 10 (esophageal, gastric, and colonic adenocarcinomas) of 170 metastatic somatic tumors demonstrated focally weak SALL4 reactivity (<25% tumor cells).

CONCLUSIONS

SALL4 is a novel sensitive and highly specific marker for metastatic germ cell tumors, and is particularly useful for detecting metastatic yolk sac tumors.

Intracranial leptomeningeal metastasis from thymic carcinoma: case report and review

BACKGROUND

Thymic carcinoma is an uncommon malignant tumor of the anterior mediastinum. Meningeal metastasis from this type of neoplasm is extraordinarily rare and the prognosis is abysmal.

CASE DESCRIPTION

This article presents the case of a 45-year-old man with known metastatic thymic carcinoma who presented with intractable headaches. An MRI scan was highly suggestive of a meningioma, and it was initially suspected that this patient had 2 primary tumors. Surgical resection of the mass both demonstrated a metastatic thymic lesion and ameliorated the patient's quality of life.

CONCLUSION

The authors report a case of intracranial meningeal metastasis from a lymphoepithelioma-like poorly differentiated metastatic thymic carcinoma, which was treated by resection and WBRT. A review of the current literature revealed no other cases of this uncommon alhistologic subtype of thymic carcinoma metastatic to the cranium. The incidence, histologic classification of subtypes, and treatment are discussed. This case also illustrates the importance of maintaining a high degree of suspicion for a metastasis in patients with known primary malignancy who present with an MRI highly suspicious for meningioma.

Diagnostic value of markers M2A, OCT3/4, AP-2γ, PLAP and c-KIT in the detection of extragonadal seminomas

AIMS

To compare the suitability of new seminoma markers including transcription factors AP-2gamma, OCT3/4 and M2A for detection of metastatic and extragonadal seminomas with the two well-known markers c-KIT and PLAP.

MATERIALS AND METHODS

The immunohistochemical distribution of PLAP, c-KIT, M2A, AP-2gamma and OCT3/4 was examined in two pineal germinomas, 28 metastatic seminomas and 10 of their testicular primaries. Evaluation of specificity was achieved by additional tissue array studies on 75 malignancies other than germ cell tumours (GCT). Clinical data including serum PLAP were available in 18 patients.

RESULTS

Compared with other markers, significantly better staining results were observed with antibodies to M2A and AP-2gamma in all seminomatous GCT. In contrast, the staining pattern with antibodies to c-KIT, PLAP and OCT3/4 was variable or absent. The lowest specificity was obtained with c-KIT, which was expressed in a variety of non-GCT. The only M2A+ mesothelioma expressed no other seminoma markers. No correlation between serum PLAP level and tissue PLAP expression was found.

CONCLUSIONS

M2A and AP-2gamma are the most sensitive markers for seminoma metastases or primary extragonadal seminomas. Combination of these markers provides highly specific and clear results for detection of a seminomatous GCT.