A Wolf in Sheep's Clothing: Collision of Melanoma and Keratoacanthoma.

Collision tumors consisting of melanoma and squamous cell carcinoma are very rare. We present the case of a deceptive hyperkeratotic nodule on the forearm of a 72-year-old woman, which clinically appeared to be a squamous cell carcinoma, keratoacanthoma type. Histological examination surprisingly revealed a coexisting epithelioid melanoma. Thus, this case report shows the importance of an early histopathological and immunohistochemical workup to prevent unnecessary diagnostic and therapeutic delay with negative effects on prognosis.

Protein tyrosine phosphatase nonreceptor type 2 controls colorectal cancer development.

Protein tyrosine phosphatase nonreceptor type 2 (PTPN2) recently emerged as a promising cancer immunotherapy target. We set out to investigate the functional role of PTPN2 in the pathogenesis of human colorectal carcinoma (CRC), as its role in immune-silent solid tumors is poorly understood. We demonstrate that in human CRC, increased PTPN2 expression and activity correlated with disease progression and decreased immune responses in tumor tissues. In particular, stage II and III tumors displayed enhanced PTPN2 protein expression in tumor-infiltrating T cells, and increased PTPN2 levels negatively correlated with expression of PD-1, CTLA4, STAT1, and granzyme A. In vivo, T cell- and DC-specific PTPN2 deletion reduced tumor burden in several CRC models by promoting CD44+ effector/memory T cells, as well as CD8+ T cell infiltration and cytotoxicity in the tumor. In direct relevance to CRC treatment, T cell-specific PTPN2 deletion potentiated anti-PD-1 efficacy and induced antitumor memory formation upon tumor rechallenge in vivo. Our data suggest a role for PTPN2 in suppressing antitumor immunity and promoting tumor development in patients with CRC. Our in vivo results identify PTPN2 as a key player in controlling the immunogenicity of CRC, with the strong potential to be exploited for cancer immunotherapy.

Role of intravoxel incoherent motion parameters in gastroesophageal cancer: relationship with 18F-FDG-positron emission tomography, computed tomography perfusion and magnetic resonance perfusion imaging parameters.

BACKGROUND: Identification of pretherapeutic predictive markers in gastro-esophageal cancer is essential for individual-oriented treatment. This study evaluated the relationship of multimodality parameters derived from intravoxel incoherent motion method (IVIM), 18F-FDG-positron emission tomography (PET), computed tomography (CT) perfusion and dynamic contrast enhanced magnetic resonance imaging (MRI) in patients with gastro-esophageal cancer and investigated their histopathological correlation. METHODS: Thirty-one consecutive patients (28 males; median age 63.9 years; range 37-84 years) with gastro-esophageal adenocarcinoma (N.=22) and esophageal squamous cell carcinoma (N.=9) were analyzed. IVIM parameters: pseudodiffusion (D*), perfusion fraction (fp), true diffusion (D) and the threshold b-value (bval); PET-parameters: SUVmax, metabolic tumor volume (MTV) and total lesion glycolysis (TLG); CT perfusion parameters: blood flow (BF), blood volume (BV) and mean transit time (MTT); and MR perfusion parameters: time to enhance, positive enhancement integral, time-to-peak (TTP), maximum-slope-of-increase, and maximum-slope-of-decrease were determined, and correlated to each other and to histopathology. RESULTS: IVIM and PET parameters showed significant negative correlations: MTV and bval (rs =-0.643, P=0.002), TLG and bval (rs=-0.699, P<0.01) and TLG and fp (rs=-0.577, P=0.006). Positive correlation was found for TLG and D (rs=0.705, P=0.000). Negative correlation was found for bval and staging (rs=0.590, P=0.005). Positive correlation was found for positive enhancement interval and BV (rs=0.547, P=0.007), BF and regression index (rs=0.753, P=0.005) and for time-to-peak and staging (rs=0.557, P=0.005). CONCLUSIONS: IVIM parameters (bval, fp, D) provide quantitative information and correlate with PET parameters (MTV, TLG) and staging. IVIM might be a useful tool for additional characterization of gastro-esophageal cancer.

The Oxysterol Synthesising Enzyme CH25H Contributes to the Development of Intestinal Fibrosis.

Intestinal fibrosis and stenosis are common complications of Crohn's disease [CD], frequently requiring surgery. Anti-inflammatory strategies can only partially prevent fibrosis; hence, anti-fibrotic therapies remain an unmet clinical need. Oxysterols are oxidised cholesterol derivatives with important roles in various biological processes. The enzyme cholesterol 25-hydroxylase [CH25H] converts cholesterol to 25-hydroxycholesterol [25-HC], which modulates immune responses and oxidative stress. In human intestinal samples from CD patients, we found a strong correlation of CH25H mRNA expression with the expression of fibrosis markers. We demonstrate reduced intestinal fibrosis in mice deficient for the CH25H enzyme, using the sodium dextran sulphate [DSS]-induced chronic colitis model. Additionally, using a heterotopic transplantation model of intestinal fibrosis, we demonstrate reduced collagen deposition and lower concentrations of hydroxyproline in CH25H knockouts. In the heterotopic transplant model, CH25H was expressed in fibroblasts. Taken together, our findings indicate an involvement of oxysterol synthesis in the pathogenesis of intestinal fibrosis.

Transplantation of Human Intestine Into the Mouse: A Novel Platform for Study of Inflammatory Enterocutaneous Fistulas.

BACKGROUND AND AIMS: Enteric fistulas represent a severe and medically challenging comorbidity commonly affecting Crohn's disease [CD] patients. Gut fistulas do not develop in animal models of the disease. We have used transplantation of the human fetal gut into mice as a novel platform for studying inflammatory enterocutaneous fistulas. METHODS: Human fetal gut segments were transplanted subcutaneously into mature SCID mice, where they grew and fully developed over the course of several months. We first analysed the resident immune cells and inflammatory response elicited by systemic lipopolysaccharide [LPS] in normal, fully developed human gut xenografts. Thereafter, we used immunostaining to analyse fully developed xenografts that spontaneously developed enterocutaneous fistulas. RESULTS: Resident human innate and adaptive immune cells were demonstrated in gut xenografts during steady state and inflammation. The expression of human IL-8, IL-1ß, IL-6, TNF-α, A20, and IkBα was significantly elevated in response to LPS, with no change in IL-10 gene expression. Approximately 17% [19/110] of fully developed subcutaneous human gut xenografts spontaneously developed enterocutaneous fistulas, revealing striking histopathological similarities with CD fistula specimens. Immunohistochemical analyses of fistulating xenografts revealed transmural lymphocytic enteritis associated with massive expansion of resident human CD4+ lymphocytes and their migration into the intraepithelial compartment. Regionally, mucosal epithelial cells assumed spindle-shaped mesenchymal morphology and formed fistulous tracts towards chronic non-healing wounds in the host mouse skin overlying the transplants. CONCLUSIONS: Inflammation and fistulas developed in human gut xenografts lacking IL-10 gene response. This novel model system will enable systematic studies of the inflamed and fistulating human gut in live animals.

WITHDRAWN: Evaluation of multifunctional imaging parameters in gastro-oesophageal cancer using F-18-FDG-PET/CT with integrated perfusion CT.

Ahead of Print article withdrawn by publisher.

Maturation of tertiary lymphoid structures and recurrence of stage II and III colorectal cancer.

Tertiary lymphoid structures (TLS) are associated with favorable outcome in non-metastatic colorectal carcinoma (nmCRC), but the dynamics of TLS maturation and its association with effective anti-tumor immune surveillance in nmCRC are unclear. Here, we hypothesized that not only the number of TLS but also their composition harbors information on recurrence risk in nmCRC. In a comprehensive molecular, tissue, laboratory, and clinical analysis of 109 patients with stage II/III nmCRC, we assessed TLS numbers and degree of maturation in surgical specimens by multi-parameter immunofluorescence of follicular dendritic cell (FDC) and germinal center (GC) markers. TLS formed in most tumors and were significantly more prevalent in highly-microsatellite-instable (MSI-H) and/or BRAF-mutant nmCRC. We could distinguish three sequential TLS maturation stages which were characterized by increasing prevalence of FDCs and mature B-cells: [1] Early TLS, composed of dense lymphocytic aggregates without FDCs, [2] Primary follicle-like TLS, having FDCs but no GC reaction, and [3] Secondary follicle-like TLS, having an active GC reaction. A simple integrated TLS immunoscore reflecting these parameters identified a large subgroup of nmCRC patients with a very low risk of recurrence independently of clinical co-variables such as ECOG performance status, age, stage, and adjuvant chemotherapy. We conclude that (1) mismatch repair and BRAF mutation status are associated with the formation of TLS in nmCRC, (2) TLS formation in nmCRC follows sequential maturation steps, culminating in germinal center formation, and (3) this maturation process harbors important prognostic information on the risk of disease recurrence.

Expression of C-KIT, CD24, CD44s, and COX2 in benign and non-invasive apocrine lesions of the breast.

Benign apocrine metaplasia (AM) of the adult breast is a very common, but enigmatic lesion. It has been speculated that AM might be a precursor of malignancy or an indicator of a susceptibility of the breast tissue to develop neoplasia, mainly based on comparing the frequency of AM in breast cancer and non-breast cancer patients [1]. Studies using comparative genomic hybridization have supported this by showing similar molecular alterations in benign and malignant apocrine lesions [2]. Few studies, however, have compared expression of biomarkers involved in tumor progression in AM and progressively more advanced atypical apocrine lesions. The expression of C-KIT, COX2, CD24, and CD44s was evaluated by immunohistochemistry in formalin-fixed, paraffin-embedded material of 9 AM, 20 apocrine ductal intraepithelial neoplasia (DIN1c-3) and 40 atypical apocrine lesions (not qualifying for DIN1c-3) and compared to expression of the same biomarkers in adjacent normal ductal epithelium. Of the 66 apocrine lesions, 62 (94 %) did not express C-KIT compared to 4/63 (6 %) of the normal glands (Fisher's exact, p < 0.001). COX2 was expressed in a significantly higher proportion of apocrine lesions than of normal glands (49 vs. 14 %, p < 0.001), and the number of apocrine lesions positive for CD24 was found to be higher with increasing aggressiveness of the lesions (Spearman, p < 0.001). In conclusion, benign and non-invasive proliferative apocrine lesions of the breast display immuno-phenotypical characteristics previously ascribed mainly to malignant transformation. This could lend support to the theory that AM is an early step towards malignant transformation, albeit associated with slow progression to carcinoma.

New Onset, Aggravation and Recurrence of Crohn's Disease upon Treatment with Three Different Tumor Necrosis Factor Inhibitors.

Tumor necrosis factor (TNF) is a major cytokine in the pathogenesis of inflammatory bowel disease (IBD), and TNF inhibition is a cornerstone of contemporary IBD therapy. However, paradoxical induction of IBD has recently been reported upon treatment of rheumatologic disorders with TNF inhibitors. In previous cases, induction of IBD was associated with one single drug and IBD was successfully managed by switching TNF inhibitors. We report the case of a patient with juvenile rheumatoid arthritis under long-term treatment with etanercept. After switching TNF inhibition to adalimumab, symptoms of Crohn's disease (CD) occurred and the diagnosis of CD was established by endoscopy. Further treatment with adalimumab and subsequently infliximab aggravated the abdominal symptoms, necessitating ileocecal resection, after which symptoms resolved for several months. Etanercept treatment due to recurrent rheumatologic symptoms was followed by recurrent CD symptoms and findings, which resolved upon discontinuation of etanercept. This case suggests that induction, aggravation and recurrence of IBD can be rare class effects of TNF inhibition.

Influence of pT3 subgroups on outcome of R0-resected colorectal tumors.

OBJECTIVE: Evaluate whether depth of infiltration within T3 colorectal tumors influences long-term oncologic outcome. PATIENTS AND METHODS: Patients with stage pT3 colon and rectal tumors were divided into four subgroups according to the depth of infiltration. The influence on overall and disease-free survival was tested for each subgroup and compared in univariate and multivariate analyses. RESULTS: A total of 368 patients were evaluated, with a median follow-up time of 92.5 months. In 181 patients with colon cancer 5- and 10-year overall survival rates were 82.7% and 65.0%, respectively, and 5- and 10-year disease-free survival rates were 80.9% and 64.4%, respectively. For 187 patients, rectal cancer 5- and 10-year overall survival rates were 69.0% and 50.5%, respectively, and disease-free survival rates were 61.3% and 47.5%, respectively. In either colon or rectal cancer, different pT3 categories showed neither a statistically significant influence on survival nor the occurrence of local or distant recurrence in univariate and multivariate analyses; however, higher pT3 subgroups had a significant influence on lymph node involvement and vessel invasion in patients with rectal cancer. CONCLUSIONS: Subdivision of pT3 tumors in colon cancer based on depth of infiltration does not provide additional information about prognosis. In rectal cancer, T3 substages were associated with lymph node involvement; however, we could not demonstrate an impact on recurrence or survival.

Chromosomal aberrations as detected by array comparative genomic hybridization in early low-grade intraepithelial neoplasias of the breast.

AIMS: Low-grade flat ductal intraepithelial neoplasia (DIN1a, flat epithelial atypia) is one of the earliest morphologically recognizable neoplastic lesions of the breast. Frequently, it occurs concomitantly with lobular intraepithelial neoplasia (LIN). We aimed to elucidate chromosomal aberrations in these early neoplastic breast lesions with the use of array comparative genomic hybridization analysis. METHODS AND RESULTS: Laser capture microdissection of 12 archival formalin-fixed, paraffin-embedded specimens harbouring foci of both DIN1a and LIN was performed. All analysed cases of DIN1a and LIN showed chromosomal gains and losses. The aberration encountered most often was loss of 16q, noted in seven DIN1a (70% of those successfully examined) and 10 LIN (91%) cases. The next most common alteration was a gain on 1q, noted in four DIN1a (40%) and seven LIN (64%) cases. CONCLUSIONS: The results show concurrent chromosomal aberrations of 1q gains and 16q losses in several cases with coexisting LIN and DIN1a. These aberrations are known to be common in low-grade invasive (ductal and lobular) carcinomas as well as in more advanced (conventional) types of low-grade ductal intraepithelial neoplasia (DIN) (low-grade ductal carcinoma in situ). Our results raise the possibility of similar molecular-genetic pathways in coexisting LIN and low-grade flat DIN.

EGFR expression in urothelial carcinoma of the upper urinary tract is associated with disease progression and metaplastic morphology.

EGFR represents a promising therapeutic target in urothelial cancer (UC). Our study aimed to investigate the clinicopathological significance of EGFR in upper urinary tract UC. EGFR was immunohistochemically assessed (EGFR pharmDX kit(TM)) in 268 consecutive tumours using a tissue microarray technique and correlated with other histopathological parameters as well as patient outcome. EGFR immunoreactivity was observed in 140/253 (55%) evaluable UCs and was associated with high tumour stage (47% pTa/pT1 vs 66% pT2-pT4; p=0.003) and high tumour grade (45% low grade vs 67% high grade; p<0.001). In addition, EGFR expression was associated with metaplastic squamous and/or glandular differentiation (p<0.001). EGFR staining intensity was 1+ in 49%, 2+ in 31%, and 3+ in 20% of cases. EGFR 3+ staining intensity was associated with the occurrence of metastatic disease by univariate analysis (p=0.016). Multivariate analysis, however, proved only pT stage >1 (p<0.001) and high tumour grade (p<0.001) to be independent predictors of patient outcome. In conclusion, EGFR was significantly associated with advanced disease and metaplastic squamous and/or glandular differentiation. Since UCs with metaplastic morphology have been shown to be more resistant to conventional radiotherapy or chemotherapy, the strikingly strong EGFR expression in these tumours may offer a new perspective for affected patients.

Tumor necrosis as prognostic indicator in transitional cell carcinoma of the upper urinary tract.

PURPOSE: The clinicopathological features predictive of outcome in patients with upper urinary tract transitional cell carcinoma are not clearly established. We analyzed the prognostic impact of tumor necrosis with respect to metastasis-free survival. MATERIALS AND METHODS: The presence of focal (10% or less of the tumor area) and extensive (greater than 10% of the tumor area) coagulative tumor necrosis was retrospectively reevaluated in 268 cases of consecutive upper urinary tract transitional cell carcinoma and correlated with outcome. RESULTS: Overall tumor necrosis was noted in 113 of 268 (42.2%) cases of transitional cell carcinoma with 63 (23.5%) showing focal and 50 (18.7%) showing extensive necrosis, respectively. Tumor necrosis was associated with high tumor stage (p <0.001) and high tumor grade (p <0.001). In addition, tumor necrosis was more common in pelvic tumors compared with ureteral tumors (p <0.001). Actuarial 5-year metastasis-free survival rates for patients with transitional cell carcinoma with extensive, focal and lacking necrosis were 24%, 45% and 78%, respectively (log rank test p <0.001). Multivariate analysis proved pT stage greater than 1 (p <0.001, RR 6.04, 95% CI 2.82-12.93), high tumor grade (p <0.001, RR 3.37, 95% CI 1.65-6.89) and extensive tumor necrosis as independent predictors of poor patient outcome (p = 0.02, RR 1.82, 95% CI 1.09-3.05). CONCLUSIONS: The presence of extensive tumor necrosis proved to be an additional histological variable with an independent influence on metastasis-free survival in patients with upper urinary tract transitional cell carcinoma. Its assessment is readily applicable in routine sections and should thus be commented upon separately in the pathology report.

Mammary NOS-type sarcoma with CD10 expression: a rare entity with features of myoepithelial differentiation.

We present an extensive immunohistochemical analysis of 7 mammary sarcomas that did not fit into any specific soft tissue sarcoma category. Histologically, they were composed of spindle cells with highly pleomorphic nuclei and abundant mitoses. Our immunohistochemical antibody panel included pan-cytokeratin (CK), basal cell type CKs (34betaE12, CK5/6, CK14, CK17) and vimentin antibodies, antibodies to established (SMA, CD10, p63, S-100, maspin, calponin, GFAP, SM-myosin), and novel (CD29, 14-3-3sigma) myoepithelial markers, as well as antibodies to CD34, desmin, h-caldesmon, steroid receptors (estrogen, progesterone, androgen), and EGFR (Her-1). Whereas CKs, CD34, desmin, and h-caldesmon were not expressed, all tumors were positive for CD10 and vimentin. CD29 and SMA were observed in 3 cases each (43%), and p63 and calponin in 2 cases each (29%). Other myoepithelial markers and steroid receptors were absent, except androgen receptors, which were expressed in one sarcoma. Five sarcomas showed positivity for EGFR. The distinction of specific, histogenetically defined sarcoma entities (such as leiomyosarcoma, angiosarcoma, liposarcoma) from NOS-type sarcoma with CD10 expression is usually clear-cut because the former exhibit a characteristic histomorphology and immunoprofile. Phyllodes tumors with stromal overgrowth or recurrent phyllodes tumors lacking epithelial structures as well as periductal stromal sarcomas can be ruled out by their frequent expression of CD34 and negativity for myoepithelial markers. The most important differential diagnosis is sarcomatoid metaplastic carcinoma because its treatment includes axillary lymphadenectomy. Since some NOS-type sarcomas with CD10 expression and most metaplastic carcinomas show positivity for CD29, SMA, and p63, differential diagnosis can be extremely difficult and requires extensive immunohistochemical evaluation for CKs and additional myoepithelial markers such as S-100, 14-3-3sigma, and maspin. The immunophenotype of NOS-type sarcomas with CD10 expression suggests that these neoplasms represent a mammary sarcoma variant with myoepithelial features.

Alpha-methylacyl-CoA racemase (AMACR/P504S) protein expression in urothelial carcinoma of the upper urinary tract correlates with tumour progression.

Alpha-methylacyl-CoA racemase (AMACR/P504S) is a useful biomarker of prostate cancer. We evaluated the expression of AMACR in upper urinary tract urothelial carcinomas with respect to associations with tumour stage, grade and metastasis-free survival. A total of 268 tumours were investigated immunohistochemically using a tissue microarray technique. AMACR expression was noted in 127 of 261 (48.7%) evaluated tumours and was associated with high tumour stage [58 of 139 (41.7%) pTa/pT1 vs. 69 of 122 (56.6%) pT2-pT4, P=0.019] and high tumour grade [44 of 137 (32.1%) low vs. 83 of 124 (66.9%) high grade, P<0.001]. In addition, AMACR expression was associated with the presence of tumour necrosis (P<0.001) and marked stromal desmoplasia (P=0.0026). This correlation indicates that increased AMACR expression might be related to hypoxia-induced changes in cancer cell metabolism, such as increased dependence on fatty acid oxidation for energy generation. Progressive disease was observed in 73 of 183 (39.9%) patients with solitary invasive carcinomas and was associated with AMACR expression (P=0.017). Multivariate analysis, however, proved only pT-stage >1 (P<0.001) and high tumour grade (P<0.001) to be independent predictors of patient outcome. In conclusion, AMACR expression correlated with advanced tumour stage and grade and may serve as an additional prognostic indicator in upper urinary tract urothelial cancer.

Ovarian granulosa cell tumors frequently express EGFR (Her-1), Her-3, and Her-4: An immunohistochemical study.

OBJECTIVE: Up to 50% of patients with ovarian granulosa cell tumors (GCTs) will develop recurrences; some of these recurrences can be seen as late as 30 years following the initial surgical treatment. Combined chemotherapy and radiotherapy are currently used for patients with advanced or recurrent disease. The aim of this study was to investigate the possible eligibility of patients with GCTs for anti-Her therapy. METHODS: The immunohistochemical expression of EGFR (Her-1), Her-2, Her-3, and Her-4 was analyzed in a group of ovarian GCTs encompassing 38 adult type and 2 juvenile type. RESULTS: Thirty-one cases (77.5%) were positive for at least one of the receptors EGFR (Her-1), Her-3, and Her-4. Twenty-six out of 40 (65%) GCTs showed positive reaction for EGFR (Her-1). Eight tumors (20%) were exclusively positive for EGFR (Her-1). None of 40 cases showed a positive reaction for Her-2. Positive reactions for Her-3 and Her-4 were observed in 18 (45%) and 23 (57.5%) tumors. Only one case (2.5%) was exclusively positive for Her-4. Four tumors (10%) showed positivity for Her-3 and Her-4 but were negative for EGFR (HER-1). While one of the two JGCTs was negative for all members of the Her-family, one showed reactivity for EGFR (Her-1), Her-3, and Her-4. CONCLUSION: In this study, most of the ovarian GCTs express at least one of the receptors EGFR (Her-1), Her-3, and Her-4. These findings provide some evidence to further explore the potential use of agents targeting these receptors (particularly EGFR) in the treatment of ovarian GCTs.

Comparison and validation of simple noninvasive tests for prediction of fibrosis in chronic hepatitis C.

Liver biopsy is recommended before antiviral treatment, particularly for patients with hepatitis C virus (HCV) genotype 1 infection, but it may cause complications and is limited by sampling error. Several non-invasive tests comprising routine laboratory parameters (simple fibrosis tests) have been proposed to predict fibrosis in chronic HCV. The aim of the current study was to validate and compare the diagnostic accuracies of the simple fibrosis tests, aspartate aminotransferase (AST)/alanine aminotransferase (ALT) ratio (AAR), cirrhosis discriminant score (CDS), age-platelet (AP) index, Pohl score, AST-to-platelet ratio index (APRI), and platelet count per se. Staging was performed in liver biopsy specimens of 194 treatment-naive patients with chronic HCV according to Ishak et al. by two independent pathologists. Receiver operating characteristic curve analysis showed comparable diagnostic accuracies of CDS, AP index, APRI, and platelet count for prediction of significant fibrosis (F3-F6) (area under the ROC curve [AUROC], 0.71, 0.74, 0.80, and 0.71, respectively; pathologist A) and for prediction of cirrhosis (F5-F6) (AUROC, 0.91, 0.91, 0.90, and 0.89, respectively; pathologist A). Diagnostic accuracy of APRI for prediction of significant fibrosis was superior to that of AAR (P < .05). Significant fibrosis was reliably predicted by APRI > or = 1.5 and platelet count <150 x10(9)/L in 24% and 22% of the patients, respectively, whereas cirrhosis was reliably excluded by APRI <2.0 and platelet count > or = 150 x10(9)/L in 85% and 78% of the patients, respectively. In conclusion, simple fibrosis tests may render liver biopsy unnecessary only in a minority of patients with chronic HCV. Improved serum fibrosis markers with greater sensitivity for severe fibrosis or cirrhosis are needed.

Metaplastic breast carcinomas: are they of myoepithelial differentiation?: immunohistochemical profile of the sarcomatoid subtype using novel myoepithelial markers.

We investigated 20 spindle cell (sarcomatoid) metaplastic carcinomas (MCs) without squamous differentiation. In addition, five high-grade phyllodes tumors were assessed for comparison. Our immunohistochemical antibody panel included pan-cytokeratin (CK), low molecular weight CK (CK8/18), four basal cell type CKs (34betaE12, CK5/6, CK14, and CK17), vimentin antibodies, as well as antibodies to established (SMA, CD10, p63, S-100, maspin, calponin, GFAP, SM-myosin), and novel (CD29, 14-3-3sigma) myoepithelial markers. Sixteen of the 20 tumors (80%) expressed at least two markers of the combination CD10/p63/SMA. S-100 detected 1 case negative for CD10/p63/SMA and 3 cases that only expressed one marker of this combination. While 18 MCs (90%) were positive for CD29, 14-3-3sigma (11 cases) and maspin (9 cases) were observed in 55% and 45%, respectively. Antibodies to pan-CK and the basal cell type CKs were strongly reactive in 12 tumors (60%), but in 6 cases (30%) positivity for these markers was weak and only focal; 2 MCs showed no positivity for CK. The stromal component of all phyllodes tumors was positive for vimentin, whereas all other investigated markers were absent except for focal p63 and CD10 expression in 1 case each. Our findings convincingly show a myoepithelial immunophenotype in sarcomatoid MCs, which is demonstrated by the presence of basal cell type CKs and the combination of the established myoepithelial markers CD10, p63, SMA, and S-100. We conclude that tumors with weak or even absent CK expression should only be diagnosed as primary sarcomas of the breast after exclusion of a myoepithelial immunophenotype. CD29 and 14-3-3sigma represent valuable novel myoepithelial markers in these diagnostically difficult cases.