Editors: Rouzan Karabakhtsian, MD, PhD, professor of pathology and director of the Women’s Health Pathology Fellowship, Albert Einstein College of Medicine, Montefiore Medical Center, Bronx, NY; Nicole Panarelli, MD, associate professor of pathology, Albert Einstein College of Medicine, Montefiore Medical Center; Shaomin Hu, MD, PhD, gastrointestinal/liver pathology fellow, University of Chicago; and S. Emily Bachert, MD, pathology resident, Department of Pathology and Laboratory Medicine, University of Kentucky, Lexington.
DNAJB1-PRKACA fusions in fibrolamellar hepatocellular carcinoma
February 2020—Recently discovered DNAJB1-PRKACA oncogenic fusions have been considered diagnostic for fibrolamellar hepatocellular carcinoma. The authors conducted a study in which they described six pancreatobiliary neoplasms with PRKACA fusions, five of which harbored the DNAJB1-PRKACA fusion. All neoplasms were subjected to a hybridization capture-based next-generation sequencing assay (MSK-Impact) that identifies sequence mutations, copy number alterations, and selected structural rearrangements involving 410 or more genes (n = 6) and/or to a custom targeted, RNA-based panel (MSK-Fusion) that uses Archer Anchored Multiplex PCR technology and next-generation sequencing to detect gene fusions in 62 genes (n = 2). Selected neoplasms also underwent FISH analysis, albumin mRNA in situ hybridization, and arginase-1 IHC labeling (n = 3). Five neoplasms were pancreatic and one arose in the intrahepatic bile ducts. All of them revealed at least focal oncocytic morphology. Three cases were diagnosed as intraductal oncocytic papillary neoplasms and three as intraductal papillary mucinous neoplasms with mixed oncocytic and pancreatobiliary or gastric features. Four cases had an invasive carcinoma component composed of oncocytic cells. Five cases revealed DNAJB1-PRKACA fusions and one revealed an ATP1B1-PRKACA fusion. None of the cases tested were positive for albumin or arginase-1. The authors concluded that these data prove that DNAJB1-PRKACA fusion is neither exclusive to nor diagnostic for fibrolamellar hepatocellular carcinoma and that caution should be exercised in diagnosing liver tumors with DNAJB1-PRKACA fusions as fibrolamellar hepatocellular carcinoma, particularly if a pancreatic lesion is present. Moreover, considering that DNAJB1-PRKACA fusions lead to upregulated protein kinase activity and that this upregulated activity has a significant role in tumorigenesis of fibrolamellar hepatocellular carcinoma, protein kinase inhibition could have therapeutic potential for treating these pancreatobiliary neoplasms once a suitable drug is developed.
Vyas M, Hechtman JF, Zhang Y, et al. DNAJB1-PRKACA fusions occur in oncocytic pancreatic and biliary neoplasms and are not specific for fibrolamellar hepatocellular carcinoma. Mod Pathol. 2019. doi:10.1038/s41379-019-0398-2.
Correspondence: Dr. O. Basturk at basturko@mskcc.org
Adequate resection margins for high-grade pleomorphic soft tissue sarcomas
The adequacy of surgical resection margins for soft tissue sarcomas is poorly defined because of the various classifications and definitions used in prior studies of heterogeneous patient cohorts and inconsistent margin sampling protocols. The authors conducted a study in which the surgical resection margins of 166 primary, high-grade, pleomorphic sarcomas of the extremity or trunk were classified according to American Joint Committee on Cancer R and Musculoskeletal Tumor Society categories, as well as by metric distance and tissue composition. None of the cases were treated with neoadjuvant therapy. Multivariable competing risk-regression models were evaluated, and optimal surgical resection margins for each classification system were defined. Minimum safe tumor clearance was 5 mm without use of adjuvant radiotherapy and 1 mm with adjuvant radiotherapy. The predictive accuracy of margin classification systems was compared by area under the receiver-operating characteristic curves generated from logistic regression of 2½-year local recurrence-free survival and other standard tests of diagnostic accuracy. The Musculoskeletal Tumor Society and margin distance classifications performed similarly, and both showed higher sensitivity and negative predictive value compared with the American Joint Committee on Cancer R classification. The prognostic power of close or positive margins in prediction models significantly increased when six or more slides were submitted for assessment of surgical resection margins. The authors concluded that surgical resection margins for soft tissue sarcoma should be reported using the Musculoskeletal Tumor Society classification or metric distance to the closest resection margin. Musculoskeletal Tumor Society wide/radical margins or tumor clearances of 5 mm, without adjuvant radiotherapy, or 1 mm, with adjuvant radiotherapy, appear to define the minimum safe surgical resection margins necessary to decrease the likelihood of local recurrence of high-grade pleomorphic sarcomas of the extremity or trunk.
Cates MM, Cates JMM. Surgical resection margin classifications for high-grade pleomorphic soft tissue sarcomas of the extremity or trunk: definitions of adequate resection margins and recommendations for sampling margins from primary resection specimens. Mod Pathol. 2019;32(10):1421–1433.
Correspondence: Dr. J. M. M. Cates at justin.m.cates@vanderbilt.edu
Intraoperative frozen section of SLN after neoadjuvant chemotherapy for breast carcinoma
False-negative intraoperative frozen section results of sentinel lymph nodes have been reported to be more common after neoadjuvant chemotherapy in the primary surgical setting. The authors evaluated sentinel lymph node (SLN) intraoperative frozen section false-negative rates in breast cancer patients treated with neoadjuvant chemotherapy and determined which, if any, histomorphologic factors are associated with false-negative results. They identified patients who had intraoperative frozen section SLN assessment following neoadjuvant chemotherapy from July 2008 to July 2017. Of 711 SLN cases, 522 were negative, 181 positive, and eight deferred. The false-negative rate was 5.4 percent (28 of 522). No false-positive results were found. Of the eight deferred cases, five were positive on permanent section and three were negative. A higher frequency of micrometastasis and isolated tumor cells was found in the false-negative cases (P < .001). A significant increase in tissue surface area was present on permanent section slides compared with intraoperative frozen section slides (P < .001), highlighting the inherent technical limitations of intraoperative frozen section and histologic undersampling of tissue, which leads to most false-negative results. The majority (25 of 28; 89 percent) of false-negative cases had metastatic foci identified exclusively on permanent sections and were not due to a true diagnostic interpretation error. False-negative cases were more frequently estrogen-receptor positive (P < .001), progesterone-receptor positive (P = .001), human epidermal growth factor receptor-2 negative (P = .009), and histologic grade one (P = .015), which most likely reflects the lower rates of pathologic complete response in these tumors. Despite its limitations, intraoperative frozen section is a reliable modality to assess SLN metastases in patients treated with neoadjuvant chemotherapy.
Grabenstetter A, Moo TA, Hajiyeva S, et al. Accuracy of intraoperative frozen section of sentinel lymph nodes after neoadjuvant chemotherapy for breast carcinoma. Am J Surg Pathol. 2019;43(10):1377–1383.
Correspondence: Dr. Anne Grabenstetter at grabensa@mskcc.org
Albumin ISH positivity in adenocarcinomas and other types of tumors
Albumin messenger RNA expression is a marker of hepatocellular differentiation. Most published data are from the review of tissue microarrays, and albumin in situ hybridization (ISH) expression across several tumor types is incompletely characterized. The authors conducted a study in which sections from 224 tumors were evaluated for albumin messenger RNA (mRNA). Immunohistochemistry was used to confirm diagnoses. Albumin ISH was performed according to manufacturer-provided instructions. Fifty-nine cases were evaluated using two commercial ISH assays. Albumin mRNA was detected in all hepatocellular carcinomas (HCCs), as well as intrahepatic cholangiocarcinomas (81 percent), lung adenocarcinomas (20 percent), gallbladder adenocarcinomas (39 percent), hepatoid pancreatic adenocarcinomas (33 percent), breast invasive ductal carcinomas (18 percent), yolk sac tumors (25 percent), and acinar cell carcinomas (29 percent). These results indicate that albumin ISH is not only positive in intrahepatic cholangiocarcinomas but may show patchy positivity in 39 percent of gallbladder adenocarcinomas and a small subset of other nonhepatocellular neoplasms, which can be a potential pitfall.
Nasir A, Lehrke HD, Mounajjed T, et al. Albumin in situ hybridization can be positive in adenocarcinomas and other tumors from diverse sites. Am J Clin Pathol. 2019;152(2):190–199.
Correspondence: Dr. R. P. Graham at graham.rondell@mayo.edu
Analysis of fumarate hydratase-deficient renal cell carcinoma
Fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) is a rare and recently described entity associated with hereditary leiomyomatosis and renal cell carcinoma syndrome. FH-deficient RCC may show variable clinical and pathologic findings but commonly presents with locally advanced and metastatic disease and has a poor prognosis. The authors conducted a study in which they identified 32 patients with FH-deficient RCC, confirmed by fumarate hydratase IHC or fumarate hydratase mutation analysis, or both, and performed a retrospective review of the clinical and pathologic features. The patients were a median age of 43 years at presentation (range, 18–69 years), and the male:female ratio was 2.2:1. The median tumor size was 6.5 cm (range, 2.5–28 cm), and 71 percent presented at stage pT3a or higher. After a median follow-up of 16 months (range, 1–118 months) in 26 patients, 19 percent showed no evidence of disease, 31 percent were alive with disease, and 50 percent were dead of disease. The vast majority of cases showed multiple histologic growth patterns, with papillary (52 percent) being the most common predominant pattern, followed by solid (21 percent), cribriform/sieve-like (14 percent), sarcomatoid (three percent), tubular (three percent), cystic (three percent), and low-grade oncocytic (three percent). Viral inclusion-like macronucleoli with perinucleolar clearing were present in 96 percent of cases. All cases were evaluated using FH IHC, and three (nine percent) cases showed retained FH expression. Nineteen cases had germline or tumor mutation analysis confirming an FH mutation, with 79 percent (11 of 14) of cases showing mutations within coding regions and 21 percent (three of 14) showing mutations within intronic splice sites. By IHC, 97 percent (32 of 33) of cases were negative for CK7, 93 percent (27 of 29) for p63, and 52 percent (15 of 29) for GATA3. All cases stained were positive for PAX8 and showed retained succinate dehydrogenase B expression. The overall findings show that FH-deficient RCC is considerably heterogenous in morphology and frequently behaves aggressively. Suspicion for this entity should be raised even in the absence of predominantly papillary architecture and characteristic nucleolar features. The authors included cases with features not commonly seen, among them four cases with predominantly cribriform/sieve-like architecture and one case with pure low-grade oncocytic morphology (nine years of clinical follow-up without evidence of disease). The authors concluded that although FH IHC is useful for identifying cases of FH-deficient RCC, not all cases of FH-deficient RCC show loss of FH staining. FH mutation analysis should be considered for patients with suspicious clinical or pathologic features, even in cases with retained FH IHC expression.
Lau HD, Chan E, Fan AC, et al. A clinicopathologic and molecular analysis of fumarate hydratase-deficient renal cell carcinoma in 32 patients. Am J Surg Pathol. 2019. doi:10.1097/PAS.0000000000001372.
Correspondence: Dr. C. Kao at ckao2@stanford.edu
Parafibromin immunostaining of parathyroid tumors in clinical routine
The cell division cycle 73 gene is mutated in familial and sporadic forms of primary hyperparathyroidism, and the corresponding protein product, parafibromin, has been proposed as an adjunct immunohistochemical marker for identifying cell division cycle 73 mutations and parathyroid carcinoma. The authors presented data from their experiences using parafibromin IHC in parathyroid tumors since the marker was implemented as part of the clinical routine at their institution in 2010. A total of 2,019 parathyroid adenomas, atypical adenomas, and carcinomas were diagnosed in their department, and parafibromin staining was ordered for 297 cases with an initial suspicion of malignant potential to avoid excessive numbers of false-positives. The most common inclusion criteria for IHC were marked tumor weight (146 cases), fibrosis (77 cases), and marked pleomorphism (58 cases). Two hundred thirty-eight cases were informatively stained, and partial or complete loss of nuclear parafibromin immunoreactivity was noted in 44 cases—10 of 182 adenomas (five percent), 27 of 46 atypical adenomas (59 percent), and seven of 10 carcinomas (70 percent)—with positive and negative predictive values of 85 and 90 percent, respectively, for detecting atypical adenomas/carcinomas versus adenomas, and 18 and 98 percent, respectively, for carcinomas versus atypical adenomas/adenomas. Male patients with highly proliferative tumors were overrepresented among cases with aberrant parafibromin IHC, and carcinomas more frequently harbored parafibromin aberrancies than atypical adenomas and adenomas (P < .001). The authors concluded that the primary strength of parafibromin IHC is its ability to serve as a marker for ruling out malignancy.
Juhlin CC, Nilsson IL, Lagerstedt-Robinson K, et al. Parafibromin immunostainings of parathyroid tumors in clinical routine: a near-decade experience from a tertiary center. Mod Pathol. 2019;32(8):1082–1094.
Correspondence: Dr. C. C. Juhlin at christofer.juhlin@ki.se