Daphne Ang

Immunohistochemical algorithm for differentiation of lung adenocarcinoma and squamous cell carcinoma based on large series of whole-tissue sections with validation in small specimens

Immunohistochemistry is increasingly utilized to differentiate lung adenocarcinoma and squamous cell carcinoma. However, detailed analysis of coexpression profiles of commonly used markers in large series of whole-tissue sections is lacking. Furthermore, the optimal diagnostic algorithm, particularly the minimal-marker combination, is not firmly established. We therefore studied whole-tissue sections of resected adenocarcinoma and squamous cell carcinoma (n=315) with markers commonly used to identify adenocarcinoma (TTF-1) and squamous cell carcinoma (p63, CK5/6, 34βE12), and prospectively validated the devised algorithm in morphologically unclassifiable small biopsy/cytology specimens (n=38). Analysis of whole-tissue sections showed that squamous cell carcinoma had a highly consistent immunoprofile (TTF-1-negative and p63/CK5/6/34βE12-diffuse) with only rare variation. In contrast, adenocarcinoma showed significant immunoheterogenetity for all ‘squamous markers’ (p63 (32%), CK5/6 (18%), 34βE12 (82%)) and TTF-1 (89%). As a single marker, only diffuse TTF-1 was specific for adenocarcinoma whereas none of the ‘squamous markers,’ even if diffuse, were entirely specific for squamous cell carcinoma. In contrast, coexpression profiles of TTF-1/p63 had only minimal overlap between adenocarcinoma and squamous cell carcinoma, and there was no overlap if CK5/6 was added as a third marker. An algorithm was devised in which TTF-1/p63 were used as the first-line panel, and CK5/6 was added for rare indeterminate cases. Prospective validation of this algorithm in small specimens showed 100% accuracy of adenocarcinoma vs squamous cell carcinoma prediction as determined by subsequent resection. In conclusion, although reactivity for ‘squamous markers’ is common in lung adenocarcinoma, a two-marker panel of TTF-1/p63 is sufficient for subtyping of the majority of tumors as adenocarcinomas vs squamous cell carcinoma, and addition of CK5/6 is needed in only a small subset of cases. This simple algorithm achieves excellent accuracy in small specimens while conserving the tissue for potential predictive marker testing, which is now an essential consideration in advanced lung cancer specimens.

KRAS mutations are associated with solid growth pattern and tumor-infiltrating leukocytes in lung adenocarcinoma

KRAS mutations define a clinically distinct subgroup of lung adenocarcinoma patients, characterized by smoking history, resistance to EGFR-targeted therapies, and adverse prognosis. Whether KRAS-mutated lung adenocarcinomas also have distinct histopathological features is not well established. We tested 180 resected lung adenocarcinomas for KRAS and EGFR mutations by high-sensitivity mass spectrometry-based genotyping (Sequenom) and PCR-based sizing assays. All tumors were assessed for the proportion of standard histological patterns (lepidic, acinar, papillary, micropapillary, solid, and mucinous), several other histological and clinical parameters, and TTF-1 expression by immunohistochemistry. Among 180 carcinomas, 63 (35%) had KRAS mutations (KRAS+), 35 (19%) had EGFR mutations (EGFR+), and 82 (46%) had neither mutation (KRAS−/EGFR−). Solid growth pattern was significantly over-represented in KRAS+ carcinomas: the mean±s.d. for the amount of solid pattern in KRAS+ carcinomas was 27±34% compared with 3±10% in EGFR+ (P<0.001) and 15±27% in KRAS−/EGFR− (P=0.033) tumors. Furthermore, at least focal (≥20%) solid component was more common in KRAS+ (28/63; 44%) compared with EGFR+ (2/35; 6%; P<0.001) and KRAS−/EGFR− (21/82; 26%; P=0.022) carcinomas. KRAS mutations were also over-represented in mucinous carcinomas and were significantly associated with the presence of tumor-infiltrating leukocytes and heavier smoking history. EGFR mutations were associated with non-mucinous non-solid patterns, particularly lepidic and papillary, lack of necrosis, lack of cytological atypia, hobnail cytology, TTF-1 expression, and never/light smoking history. In conclusion, extended molecular and clinicopathological analysis of lung adenocarcinomas reveals a novel association of KRAS mutations with solid histology and tumor-infiltrating inflammatory cells and expands on several previously recognized morphological and clinical associations of KRAS and EGFR mutations. Solid growth pattern was recently shown to be a strong predictor of aggressive behavior in lung adenocarcinomas, which may underlie the unfavorable prognosis associated with KRAS mutations in these tumors.

Driver mutations determine survival in smokers and never-smokers with stage IIIB/IV lung adenocarcinomas.

The authors previously demonstrated that never‐smokers with stage IIIB/IV nonsmall cell lung cancer (NSCLC) lived 50% longer than former/current smokers. This observation persisted after adjusting for age, performance status, and sex. In this study, the authors hypothesized that smoking‐dependent differences in the distribution of driver mutations may explain differences in prognosis between these subgroups.

Frequent phosphatidylinositol-3-kinase mutations in proliferative breast lesions.

The phosphatidylinositol-3-kinase pathway is one of the most commonly altered molecular pathways in invasive breast carcinoma, with phosphatidylinositol-3-kinase catalytic subunit (PIK3CA) mutations in 25% of invasive carcinomas. Ductal carcinoma in situ (DCIS), benign papillomas, and small numbers of columnar cell lesions harbor an analogous spectrum of PIK3CA and AKT1 mutations, yet there is little data on usual ductal hyperplasia and atypical ductal and lobular neoplasias. We screened 192 formalin-fixed paraffin-embedded breast lesions from 75 patients for point mutations using a multiplexed panel encompassing 643 point mutations across 53 genes, including 58 PIK3CA substitutions. PIK3CA point mutations were identified in 31/62 (50%) proliferative lesions (usual ductal hyperplasia and columnar cell change), 10/14 (71%) atypical hyperplasias (atypical ductal hyperplasia and flat epithelial atypia), 7/16 (44%) lobular neoplasias (atypical lobular hyperplasia and lobular carcinoma in situ), 10/21 (48%) DCIS, and 13/37 (35%) invasive carcinomas. In genotyping multiple lesions of different stage from the same patient/specimen, we found considerable heterogeneity; most notably, in 12 specimens the proliferative lesion was PIK3CA mutant but the concurrent carcinoma was wild type. In 11 additional specimens, proliferative epithelium and cancer contained different point mutations. The frequently discordant genotypes of usual ductal hyperplasia/columnar cell change and concurrent carcinoma support a role for PIK3CA-activating point mutations in breast epithelial proliferation, perhaps more so than transformation. Further, these data suggest that proliferative breast lesions are heterogeneous and may represent non-obligate precursors of invasive carcinoma.

Mucinous breast carcinomas lack PIK3CA and AKT1 mutations

Activating point mutations in the phosphatidylinositol-3-kinase catalytic subunit (PIK3CA) are among the most common molecular defects in invasive breast cancer. Point mutations in the downstream kinase AKT1 are seen in a minority of carcinomas. These mutations are found preferentially in estrogen receptor-positive and Her2-positive breast carcinomas; however, special morphologic types of breast cancer have not been well studied. Twenty-nine cases of pure invasive mucinous carcinoma and 9 cases of ductal carcinoma with mucinous differentiation were screened for a panel of point mutations (>321 mutations in 30 genes) using a multiplex polymerase chain reaction panel with mass spectroscopy readout. In addition, associated ductal carcinoma in situ, hyperplasia, or columnar cell lesions were separately tested where available (25 lesions). In 3 invasive cases and 15 ductal carcinoma in situ/proliferative lesions, PIK3CA hotspot mutations were, instead, tested by direct sequencing. No point mutations were identified in invasive mucinous breast carcinoma. This contrasts with the 35% frequency of PIK3CA mutations in a comparative group of invasive ductal carcinomas of no special type. Interestingly, PIK3CA hotspot point mutations were identified in associated ductal carcinoma in situ (3/14) and hyperplasia (atypical ductal hyperplasia [2/3], usual ductal hyperplasia [2/3], columnar cell change [1/5]), suggesting that PIK3CA mutations may play a role in breast epithelial proliferation. This series represents the largest study, to date, of PIK3CA genotyping in mucinous carcinoma and supports the unique pathogenetics of invasive mucinous breast carcinoma.

Novel Mutations in Neuroendocrine Carcinoma of the Breast: Possible Therapeutic Targets

Primary neuroendocrine carcinoma of the breast is a rare variant, accounting for only 2% to 5% of diagnosed breast cancers, and may have relatively aggressive behavior. Mutational profiling of invasive ductal breast cancers has yielded potential targets for directed cancer therapy, yet most studies have not included neuroendocrine carcinomas. In a tissue microarray screen, we found a 2.4% prevalence (9/372) of neuroendocrine breast carcinoma, including several with lobular morphology. We then screened primary or metastatic neuroendocrine breast carcinomas (excluding papillary and mucinous) for mutations in common cancer genes using polymerase chain reaction-mass spectroscopy (643 hotspot mutations across 53 genes), or semiconductor-based next-generation sequencing analysis (37 genes). Mutations were identified in 5 of 15 tumors, including 3 with PIK3CA exon 9 E542K mutations, 2 of which also harbored point mutations in FGFR family members (FGFR1 P126S, FGFR4 V550M). Single mutations were found in each of KDR (A1065T) and HRAS (G12A). PIK3CA mutations are common in other types of breast carcinoma. However, FGFR and RAS family mutations are exceedingly rare in the breast cancer literature. Likewise, activating mutations in the receptor tyrosine kinase KDR (VEGFR2) have been reported in angiosarcomas and non–small cell lung cancers; the KDR A1065T mutation is reported to be sensitive to VEGFR kinase inhibitors, and fibroblast growth factor receptor inhibitors are in trials. Our findings demonstrate the utility of broad-based genotyping in the study of rare tumors such as neuroendocrine breast cancer.

BCR-ABL1 RT-qPCR for Monitoring the Molecular Response to Tyrosine Kinase Inhibitors in Chronic Myeloid Leukemia

The pathognomonic genetic alteration in chronic myeloid leukemia is the formation of the BCR-ABL1 fusion gene, which produces a constitutively active tyrosine kinase that drives leukemic transformation. Targeted tyrosine kinase inhibitor treatment with imatinib, nilotinib, dasatinib, bosutinib, and ponatinib is the cornerstone of modern therapy for this hematologic malignancy. Real-time quantitative RT-PCR (RT-qPCR, also RQ-PCR) of BCR-ABL1 RNA is a necessary laboratory technique for monitoring the efficacy of tyrosine kinase inhibitor therapy and quantitatively assessing minimal residual disease. The molecular response measured by BCR-ABL1 RT-qPCR assists in identifying suboptimal responses and can help inform the decision to switch to alternative therapies that may be more efficacious (or to pursue more stringent monitoring). Furthermore, the tyrosine kinase inhibitor-mediated molecular response provides valuable risk stratification and prognostic information on long-term outcomes. Despite these attributes, informed, universal, practical utilization of this well-established monitoring test will require heightened efforts by the molecular diagnostics laboratory community to adopt the standardized reporting units of the International Scale. Without widespread adoption of the International Scale, the consensus major molecular response and early molecular response treatment thresholds will not be definable, and optimal clinical outcomes for patients with chronic myeloid leukemia may not be achieved.

Frequent PIK3CA mutations in radial scars

Radial scars are breast lesions of uncertain pathogenesis that are associated with a 2-fold increased risk of breast cancer compared with that in controls. Activating point mutations in PIK3CA are found in 25% to 30% of invasive breast cancers; however, they have not previously been investigated in radial scars. We sought to evaluate radial scars for known activating point mutations commonly seen in invasive breast cancer. Sixteen surgical cases containing 22 radial scars were identified from pathology archives. Lesional tissue was macrodissected from unstained paraffin sections; genomic DNA was then extracted and screened for a panel of known hotspot mutations using polymerase chain reaction and mass spectroscopy analysis. Of the 22 radial scars, 14 (63.6%) had PIK3CA mutations (10 with H1047R mutations, 2 G1049R mutations, 1 E542K, 1 E545K). The remaining 8 lesions were wild type for all of the screened genes. Of the radial scars without epithelial atypia, 9/16 (56.3%) had PIK3CA mutations; furthermore, 5/6 (83.3%) radial scars with atypia had mutations detected. In this study, the frequency of PIK3CA mutations was notably higher than the 25% to 30% mutation frequency of invasive breast cancer. This finding raises interesting questions as to the role of PIK3CA mutations in breast cancer development. Additional larger studies are indicated to confirm and extend these observations in understanding the pathogenesis of radial scars and their relationship to breast cancer.

PIK3CA-AKT pathway mutations in micropapillary breast carcinoma.

Micropapillary carcinoma of the breast is associated with increased rates of lymph node metastasis and lymphovascular invasion. While activating point mutations in PIK3CA (encoding phosphatidylinositol-3-kinase catalytic subunit) or AKT1 are found in 25% to 30% of invasive ductal carcinomas, the mutational profile of invasive micropapillary carcinomas has not been characterized in detail. Micropapillary carcinomas, concurrent metastatic and precursor breast lesions from 19 patients were identified. Lesional tissue was punched from paraffin-tissue blocks, and genomic DNA was extracted and screened for a large panel of known hotspot mutations using multiplex polymerase chain reaction and mass-spectroscopy analysis (643 mutations in 53 genes). Hotspot point mutations were identified in 35% (7/20) of micropapillary breast carcinomas, including PIK3CA exons 7, 9 and 20 hotspots, as well as the AKT1 plekstrin homology domain mutation (E17K); mutations in TP53 and KRAS were each found in a single patient. In 6 patients, micropapillary and non-micropapillary components of the same tumor were separately tested, yielding concordant results in five; one had a wild type micropapillary component, but a PIK3CA mutation in the invasive ductal component. Concurrent lymph node metastases were mostly wild type (2/8 mutant). Accompanying ductal carcinoma in situ had point mutations in 45% (5/11), mostly concordant with invasive carcinoma; however, mutational status of other breast proliferative lesions was generally discordant with accompanying carcinoma. The rate of PIK3CA mutations in this series of micropapillary carcinomas is similar to invasive ductal carcinomas; however, there may be an enrichment of AKT1 mutations (10%). The non-micropapillary components and precursor lesions occasionally had different mutations.

Biphasic papillary and lobular breast carcinoma with PIK3CA and IDH1 mutations.

Morphologic “special types” of breast carcinomas have been recognized for many years, and their molecular and genetic properties have not been specifically studied until recently. Lobular carcinoma lacks functional E-cadherin expression but shares molecular similarities with low-grade invasive ductal carcinomas. Papillary carcinoma is relatively rare, and molecular features are just being elucidated. We report a case of concurrent invasive lobular and papillary carcinoma, the latter with extensive nodal involvement. Multiplex screening for activating point mutations identified different point mutations in the distinct morphologic components: lobular PIK3CA H1047R, papillary; PIK3CA Q546P, and IDH1 R132H. These molecular data favor coincidental “collision tumors” over clonal evolution. The IDH1 R132H point mutation is common in gliomas and acute myelogenous leukemia, but this has not been previously reported in breast carcinoma. The characterization of activating point mutations in morphologic special types of breast carcinoma may suggest avenues amenable to targeted therapy.