Fine-Needle Aspiration Biopsy of Liver Lesions Yields Higher Tumor Fraction for Molecular Studies: A Direct Comparison With Concurrent Core Needle Biopsy.

BACKGROUND: This retrospective study evaluated and compared the diagnostic accuracy and suitability of tissue specimens for advanced molecular diagnostic testing obtained via 2 different techniques for percutaneous biopsy of primary and metastatic liver tumors. PATIENTS AND METHODS: Samples from 137 patients with liver masses who underwent concurrent fine-needle aspiration biopsy with cell block (FNAB-CB) and core needle biopsy (CNB) at 2 hospitals were assessed for diagnostic accuracy, tumor fraction, and tumor cellularity. A subset of FNAB-CBs, that were deemed to have less or equal tumor cellularity compared with CNBs, had level sections performed and were reassessed for tumor cellularity. RESULTS: Diagnostic accuracy was 96% for FNAB and 93% for CNB (P=.267). In FNAB-CBs, tumor fraction was significantly higher than in CNB samples (67% vs 36%; P<.0001), whereas nontumor components were significantly lower (stromal component, 7% vs 29%; P<.0001; background benign hepatocytes, 25% vs 36%; P=.003). Additionally, in 44% of cases, FNAB-CB tumor cellularity was equal to or greater than that of the concurrent CNB. CONCLUSIONS: In the current age of personalized medicine, a minimally invasive, safe approach to obtaining adequate tissue for myriad molecular testing is paramount. We have shown that FNAB sampling is diagnostically accurate and produces higher tumor fractions than CNB. Thus, FNAB should be strongly considered as an initial sampling modality, especially for patients in whom molecular tests will determine management.

Risk prediction for local versus regional/metastatic tumors after initial ductal carcinoma in situ diagnosis treated by lumpectomy.

Among women diagnosed with ductal carcinoma in situ (DCIS), we identified factors associated with local invasive cancer (LIC) and regional/metastatic invasive cancer (RMIC) and provide 10-year risks based on clinically relevant factors. We created a retrospective, population-based cohort of 1492 women with an initial diagnosis of DCIS (1983-1996) treated by lumpectomy alone. Histological and molecular markers (Ki67, ER, PR, COX-2, p16, ERBB2) were collected on DCIS cases with a subsequent tumor (DCIS, LIC, or RMIC) and a subsample of frequency-matched controls without subsequent tumors. Competing risks methods were used to identify factors associated with LIC and RMIC and cumulative incidence methods to estimate 10-year risks for combinations of factors. Median follow-up time was 12.6 years (range 0.5-29.5 years). The overall 10-year risk of LIC (11.9 %) was higher than for RMIC (3.8 %). About half of women with initial DCIS lesions are detected by mammography and p16 negative and have a 10-year risk of LIC of 6.2 % (95 % CI 5.8-6.8 %) and RMIC of 1.2 % (95 % CI 1.1-1.3 %). Premenopausal women whose DCIS lesion was p16 positive or p16 negative and detected by palpation had high 10-year risk of LIC of 23.0 % (95 % CI 19.3-27.4 %). Ten-year risk of RMIC was highest at 22.5 % (95 % CI 13.8-48.1 %) for those positive for p16, COX-2, and ERRB2, and negative for ER, but prevalence of this group is low at 3 %. Ten-year risk of LIC and RMIC is low for the majority diagnosed with DCIS. Combinations of molecular markers and method of detection of initial DCIS lesion can differentiate women at low and high risk of LIC and RMIC.

Breast cancer version 3.2014.

Breast cancer is the most common malignancy in women in the United States and is second only to lung cancer as a cause of cancer death. The overall management of breast cancer includes the treatment of local disease with surgery, radiation therapy, or both, and the treatment of systemic disease with cytotoxic chemotherapy, endocrine therapy, biologic therapy, or combinations of these. The NCCN Guidelines specific to management of large clinical stage II and III tumors are discussed in this article. These guidelines are the work of the members of the NCCN Breast Cancer Panel. Expert medical clinical judgment is required to apply these guidelines in the context of an individual patient to provide optimal care. Although not stated at every decision point of the guidelines, patient participation in prospective clinical trials is the preferred option of treatment for all stages of breast cancer.

Genomic and transcriptional aberrations linked to breast cancer pathophysiologies.

This study explores the roles of genome copy number abnormalities (CNAs) in breast cancer pathophysiology by identifying associations between recurrent CNAs, gene expression, and clinical outcome in a set of aggressively treated early-stage breast tumors. It shows that the recurrent CNAs differ between tumor subtypes defined by expression pattern and that stratification of patients according to outcome can be improved by measuring both expression and copy number, especially high-level amplification. Sixty-six genes deregulated by the high-level amplifications are potential therapeutic targets. Nine of these (FGFR1, IKBKB, ERBB2, PROCC, ADAM9, FNTA, ACACA, PNMT, and NR1D1) are considered druggable. Low-level CNAs appear to contribute to cancer progression by altering RNA and cellular metabolism.

Breast cancer, version 3.2013: featured updates to the NCCN guidelines.

These NCCN Guidelines Insights highlight the important updates specific to the management of HER2-positive metastatic breast cancer in the 2013 version of the NCCN Clinical Practice Guidelines in Oncology for Breast Cancer. These include new first-line and subsequent therapy options for patients with HER2-positive metastatic breast cancer.

In situ analyses of genome instability in breast cancer.

Transition through telomere crisis is thought to be a crucial event in the development of most breast carcinomas. Our goal in this study was to determine where this occurs in the context of histologically defined breast cancer progression. To this end, we assessed genome instability (using fluorescence in situ hybridization) and other features associated with telomere crisis in normal ductal epithelium, usual ductal hyperplasia, ductal carcinoma in situ and invasive cancer. We modeled this process in vitro by measuring these same features in human mammary epithelial cell cultures during ZNF217-mediated transition through telomere crisis and immortalization. Taken together, the data suggest that transition through telomere crisis and immortalization in breast cancer occurs during progression from usual ductal hyperplasia to ductal carcinoma in situ.

Metastatic breast cancer, version 1.2012: featured updates to the NCCN guidelines.

These NCCN Guidelines Insights highlight the important updates/changes specific to the management of metastatic breast cancer in the 2012 version of the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Breast Cancer. These changes/updates include the issue of retesting of biomarkers (estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2) on recurrent disease, new information regarding first-line combination endocrine therapy for metastatic disease, a new section on monitoring of patients with metastatic disease, and new information on endocrine therapy combined with an mTOR inhibitor as a subsequent therapeutic option.

A Large Thyroid Fine Needle Aspiration Biopsy Cohort with Long-Term Population-Based Follow-Up.

Background: Prior studies evaluating thyroid fine needle aspiration biopsies (FNABs) have limited the calculation of risk of malignancy (ROM) to cytologic specimens with corresponding histologic specimens, and clinical follow-up for those patients who do not undergo immediate surgery has been largely disregarded. Moreover, there is marked variability in how researchers have approached thyroid FNAB statistical analyses. This study addresses the urgent need for information from a large cohort of patients with long-term clinical follow-up to more accurately determine the performance of thyroid FNAB and ROM for each diagnostic category. Methods: A retrospective review of the University of California, San Francisco (UCSF), pathology database for thyroid FNABs from January 1, 1997, to December 31, 2004, was performed. Diagnoses were coded using the 2017 The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), and patients were matched to both the UCSF cancer registry and California Cancer Registry. Data were analyzed using the Kaplan-Meier method, and stratified by TBSRTC diagnostic category. Kaplan-Meier curves were used to estimate incidence rates of malignancy, stratified by FNAB category. Cox proportional hazards models were used to determine the instantaneous ROM. Results: Initial FNABs from 2207 patients were included. Median follow-up period after the first thyroid FNAB was 13.9 years (range: 10.5-18.4 years). During follow-up, there were 279 confirmed diagnoses of thyroid malignancy. Estimates derived from Kaplan-Meier curves demonstrated that the risk of having a thyroid malignancy was low for nondiagnostic and benign categories, intermediate for atypia of undetermined significance (AUS), follicular lesion of undetermined significance (FLUS), AUS/FLUS combined, and follicular neoplasm, and high for suspicious and malignant categories. A total of 52/1575 false-negative cases (3.2%) were identified. Excluding papillary microcarcinomas, the false-negative rate was 1.5% (23/1575). No patients with a false-negative diagnosis died of thyroid cancer during the follow-up period. Conclusions: Asymptomatic patients with low-risk clinical and radiologic features and initially benign or unsatisfactory biopsy are unlikely to develop thyroid malignancy and highly unlikely to die of thyroid cancer. FNAB is highly accurate in detecting malignancy. Additional studies evaluating similar large data sets after the adoption of TBSRTC and the integration of molecular testing are needed.

Evaluating Estrogen Receptor Immunohistochemistry on Cell Blocks From Breast Cancer Patients in a Low-Resource Setting.

CONTEXT.­: Breast cancer biomarker assessment is critical in determining treatment and prognosis. In Tanzania, immunohistochemistry (IHC) is limited to surgical specimens and core biopsies. However, performing IHC on fine-needle aspiration biopsy cell blocks would offer numerous advantages. OBJECTIVE.­: To compare the performance between estrogen receptor (ER) IHC performed at Muhimbili National Hospital (MNH) in Tanzania and ER IHC performed at University of California, San Francisco (UCSF), to demonstrate feasibility of performing IHC using cell blocks in Tanzania. DESIGN.­: Patients with breast masses were recruited prospectively from the fine-needle aspiration biopsy clinic at MNH. Estrogen receptor IHC results on cell blocks, performed at both MNH and UCSF, and corresponding tissue blocks, performed at MNH, were compared to determine concordance. RESULTS.­: Eighty-six cell blocks were evaluated by ER IHC at MNH, with 41 of 86 (47.7%) positive and 45 of 86 (52.3%) negative. Among 65 UCSF and MNH cell block pairs, overall ER IHC concordance was 93.8% (61 of 65) and positive concordance was 93.5% (29 of 31) (κ = 0.88, P > .99). Among 43 paired UCSF cell blocks and MNH tissue blocks, overall ER IHC concordance was 88.3% (38 of 43) and positive concordance was 90.5% (19 of 21) (κ = 0.77, P > .99). We compared 62 MNH cell block and tissue block pairs. Overall ER IHC concordance was 90.3% and positive concordance was 87.9% (κ = 0.81, P = .69). CONCLUSIONS.­: Pairwise comparisons between ER IHC at MNH, on cell blocks and tissue blocks, with ER IHC at UCSF on cell blocks showed excellent concordance. We demonstrate that ER IHC on fine-needle aspiration biopsy specimens can be implemented in resource-constrained settings.

Molecular testing for somatic mutations improves the accuracy of thyroid fine-needle aspiration biopsy.

BACKGROUND: Thyroid fine-needle aspiration (FNA) biopsy is indeterminate or suspicious in up to 30% of cases and these patients are commonly subjected to at least a diagnostic hemithyroidectomy. If malignant on histology, a completion thyroidectomy is usually performed, which may be associated with higher morbidity. To determine the clinical utility of genetic testing in thyroid FNA biopsy, we conducted a prospective clinical trial. METHODS: Four hundred seventeen patients with 455 thyroid nodules were enrolled and had genetic testing for common somatic mutations (BRAF, NRAS, KRAS) and gene rearrangements (RET/PTC1, RET/PTC3, RAS, TRK1) by PCR and direct sequencing and by nested PCR, respectively. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of genetic testing in thyroid FNA biopsy were determined based on the histologic diagnosis. RESULTS: One hundred twenty-five of 455 thyroid nodule FNA biopsies were indeterminate or suspicious on cytologic examination. Overall, 50 mutations were identified (23 BRAF, 4 RET/PTC1, 2 RET/PTC3, 21 NRAS) in the thyroid FNA biopsies. There were significantly more mutations detected in malignant thyroid nodules than in benign (P = 0.0001). For thyroid FNA biopsies that were indeterminate or suspicious, genetic testing had a sensitivity of 12%, specificity of 98%, PPV of 38%, and NPV of 65%. CONCLUSIONS: Genetic testing for somatic mutations in thyroid FNA biopsy samples is feasible and identifies a subset of malignant thyroid neoplasms that are indeterminate or suspicious on FNA biopsy. Genetic testing for common somatic genetic alterations thus could allow for more definitive initial thyroidectomy in those with positive results.

The International Academy of Cytology Yokohama System for Reporting Breast Fine-Needle Aspiration Biopsy Cytopathology.

The International Academy of Cytology (IAC) gathered together a group of cytopathologists expert in breast cytology who, working with clinicians expert in breast diagnostics and management, have developed the IAC Yokohama System for Reporting Breast Fine-Needle Aspiration Biopsy (FNAB) Cytology. The project was initiated with the first cytopathology group meeting in Yokohama at the 2016 International Congress of Cytology. This IAC Yokohama System defines five categories for reporting breast cytology, each with a clear descriptive term for the category, a definition, a risk of malignancy (ROM) and a suggested management algorithm. The key diagnostic cytopathology features of each of the lesions within each category will be presented more fully in a subsequent atlas. The System emphasizes that the crucial requirements for diagnostic breast FNAB cytology are a high standard for the performance of the FNAB and for the making of direct smears, and well-trained experienced cytopathologists to interpret the material. The performance indicators of breast FNAB, including specificity and sensitivity, negative predictive value, positive predictive value and ROM stated in this article have been derived from the recent literature. The current practice of breast FNAB has evolved with the increasing use of ultrasound guidance and rapid on-site evaluation. Two recent publications have shown a range of ROM for the insufficient/inadequate category of 2.6-4.8%, benign 1.4-2.3%, atypical 13-15.7%, suspicious of malignancy 84.6-97.1%, and malignant 99.0-100%. The management algorithm in the System provides options because there are variations in the management of breast lesions using FNAB and core-needle biopsy in those countries utilizing the "triple test" of clinical, imaging, and FNAB assessment, and also variations in the availability of CNB and imaging in low- and middle-income countries. The System will stimulate further discussion and research, particularly in the cytological diagnostic features of specific lesions within each category and in management recommendations. This will lead to continuing improvements in the care of patients with breast lesions and possible modifications to the IAC Yokohama System.

Breast pathology guideline implementation in low- and middle-income countries.

The quality of breast healthcare delivery and the ultimate clinical outcome for patients with breast cancer are directly related to the quality of breast pathology practices within the healthcare system. The Breast Health Global Initiative (BHGI) held its third Global Summit in Budapest, Hungary from October 1 to 4, 2007, bringing together internationally recognized experts to address the implementation of breast healthcare guidelines for the early detection, diagnosis, and treatment in low-income and middle-income countries (LMCs). From this group, a subgroup of experts met to address the specific needs and concerns related to breast pathology program implementation in LMCs. Specific recommendations were made by the group and process indicators identified in the areas of personnel and training, cytology and histopathology interpretation, accuracy of pathology interpretation, pathology reporting, tumor staging, causes of diagnostic errors, use of immunohistochemical markers, and special requirements to facilitate breast conservation therapy. The group agreed that the financial burden of establishing and maintaining breast pathology services is counterbalanced by the cost savings from decreased adverse effects and excessive use of treatment resources that result from incorrect or incomplete pathologic diagnosis. Proper training in breast pathology for pathologists and laboratory technicians is critical and provides the underpinnings of programmatic success for any country at any level of economic wealth.

Guideline implementation for breast healthcare in low- and middle-income countries: diagnosis resource allocation.

A key determinant of breast cancer outcome in any population is the degree to which newly detected cancers can be diagnosed correctly so that therapy can be selected properly and provided in a timely fashion. A multidisciplinary panel of experts reviewed diagnosis guideline tables and discussed core implementation issues and process indicators based on the resource stratification guidelines. Issues were then summarized in the context of 1) clinical assessment, 2) diagnostic breast imaging, 3) tissue sampling, 4) surgical pathology, 5) laboratory tests and metastatic imaging, and 6) the healthcare system. Patient history provides important information for the clinical assessment of breast and comorbid disease that may influence therapy choices. Focused clinical breast examination and complete physical examination provide guidance on the extent of disease, the presence of metastatic disease, and the ability to tolerate aggressive therapeutic regimens. Breast imaging improves preoperative diagnostic assessment and also permits image-guided needle sampling. Diagnostic mammography was not considered mandatory in low- and middle-income countries when resources are lacking. Needle biopsy is preferred to surgical excision for the initial diagnosis of suspicious breast lesions, unless resources are unavailable. Mastectomy should never be used as a method of tissue diagnosis. The availability of predictive tumor markers, especially estrogen receptor testing, is critical when endocrine therapies are available; quality assessment of immunohistochemistry testing is important to avoid false-negative results. Incremental allocation of resources can help address economic disparities and help ensure equity in access to timely diagnosis.

Primary diagnosis of ruptured biceps tendon "Baker's-type cyst" using fine needle aspiration biopsy: A case report.

Biceps tendon rupture is generally a clinical and radiographic diagnosis, and only rarely presents to the cytopathologist for fine needle aspiration biopsy. We present a case of ruptured biceps tendon associated with a cystic mass of the upper arm that was diagnosed using fine needle aspiration biopsy, and confirmed with subsequent MRI scan. We describe the clinical presentation, cytomorphology, and immunohistochemical profile of the marked chronic inflammatory infiltrate within the synovial fluid. We also provide a discussion of the differential diagnosis for a cystic mass associated with the biceps tendon on cytology.

Cytology cases of the week: an educational tool that improves trainee exposure to cytology.

INTRODUCTION: The Accreditation Council for Graduate Medical Education requires residents to examine 1500 cytology specimens by the end of residency. Cytology cases of the week (COWs) were instituted in 2010-2011 in an effort to increase trainee exposure to cytology. MATERIALS AND METHODS: Images of 2 to 5 cases with basic clinical information are sent to residents weekly. Residents have 1 week to respond by e-mail; after which, correct answers are e-mailed. Cytology resident in-service examination (RISE) scores were used to assess the effectiveness of COWs. Additionally, a feedback survey was distributed to trainees to determine the perception of COWs as a teaching tool. RESULTS: An unpaired two-sided t test showed residents who participated in COWs scored 15.4% higher on the RISE than residents who participated minimally or not at all over the 5-year period (P < 0.05). In 2014-2015 and 2015-2016, when COWs were minimally and not at all offered, we saw a significant decrease in average cytology RISE scores compared with prior years when COWs were offered (P < 0.05). There was no correlation between percentage of correctly submitted answers for COWs and RISE scores. The vast majority (83%) of trainees reported participating in COWs for self-study, and the majority (86%) felt participation in COWs increased their cytology knowledge. Major reasons for not participating included technical challenges and time limitations. CONCLUSIONS: COWs are an effective educational tool that increase resident fund of knowledge in cytology. Residents who participate in COWs perform higher on the RISE, regardless of percentage of correctly submitted answers.

Does routine consultation of thyroid fine-needle aspiration cytology change surgical management?

BACKGROUND: Routine secondary cytologic review of thyroid gland fine-needle aspiration (FNA) specimens in patients referred from other institutions has been the recommended practice at some medical centers. We sought to determine the concordance rates between FNA interpretations at referring institutions and our center to determine if they alter surgical management. STUDY DESIGN: All thyroid gland FNAs referred to our center for cytopathologic opinion from June 2000 to August 2004 were reviewed. Patients in whom FNA biopsies were performed for thyroid cancer recurrences or core biopsies and patients in whom only a cytopathologic opinion was requested without a clinical consultation were excluded from the study. FNA results were divided into benign, indeterminate, suspicious, malignant, and nondiagnostic categories. FNA interpretations at our medical center and the referring institutions were compared with final histology results in patients who underwent operations. RESULTS: One hundred forty-seven patients had secondary review of their thyroid gland FNA specimens. The overall concordance was 82%, with the highest concordance rate in the malignant category (95%) and the lowest in the suspicious category (62%, p<0.001). The sensitivity (94% versus 92%), specificity (76% versus 56%), and positive (93% versus 87%) and negative (79% versus 69%) predictive values were all higher on secondary review. Twenty-seven patients were found to have discordant FNA interpretations. As a result of the discordant FNA result, four patients had their surgical management decisions changed. Another four patients had appropriate oncologic thyroid resection as a result of the secondary review. CONCLUSIONS: Our results suggest that routine secondary cytopathologic review of FNA specimens from referring institutions changes surgical management in some patients with thyroid neoplasms. We recommend this practice be widely used at other centers, especially for suspicious results.

Breast tumor copy number aberration phenotypes and genomic instability.

BACKGROUND: Genomic DNA copy number aberrations are frequent in solid tumors, although the underlying causes of chromosomal instability in tumors remain obscure. Genes likely to have genomic instability phenotypes when mutated (e.g. those involved in mitosis, replication, repair, and telomeres) are rarely mutated in chromosomally unstable sporadic tumors, even though such mutations are associated with some heritable cancer prone syndromes. METHODS: We applied array comparative genomic hybridization (CGH) to the analysis of breast tumors. The variation in the levels of genomic instability amongst tumors prompted us to investigate whether alterations in processes/genes involved in maintenance and/or manipulation of the genome were associated with particular types of genomic instability. RESULTS: We discriminated three breast tumor subtypes based on genomic DNA copy number alterations. The subtypes varied with respect to level of genomic instability. We find that shorter telomeres and altered telomere related gene expression are associated with amplification, implicating telomere attrition as a promoter of this type of aberration in breast cancer. On the other hand, the numbers of chromosomal alterations, particularly low level changes, are associated with altered expression of genes in other functional classes (mitosis, cell cycle, DNA replication and repair). Further, although loss of function instability phenotypes have been demonstrated for many of the genes in model systems, we observed enhanced expression of most genes in tumors, indicating that over expression, rather than deficiency underlies instability. CONCLUSION: Many of the genes associated with higher frequency of copy number aberrations are direct targets of E2F, supporting the hypothesis that deregulation of the Rb pathway is a major contributor to chromosomal instability in breast tumors. These observations are consistent with failure to find mutations in sporadic tumors in genes that have roles in maintenance or manipulation of the genome.

Pancreatoblastoma in an adult: case report and review of the literature.

A 50-year-old man presented with progressive gastrointestinal symptoms. An abdominal computed tomography scan demonstrated a 12 x 12-cm pancreatic mass involving the greater curvature of the stomach and multiple hypervascular hepatic metastases. An initial fine needle aspiration of the pancreatic mass was nondiagnostic, and a subsequent fine needle aspiration of a liver mass was read as metastatic acinar cell carcinoma. The patient underwent a palliative resection for tumor-associated pain and gastrointestinal hemorrhage that revealed a large pancreatic tumor invading through the full thickness of the colon at the splenic flexure and adherent to the posterior gastric wall. The pathology from the distal pancreatectomy, splenectomy, partial gastrectomy, partial colectomy, and cholecystectomy unexpectedly supported a diagnosis of pancreatoblastoma with evidence for squamoid corpuscles as well as areas of acinar formation. Despite multiple chemotherapy regimens, the patient's disease continued to progress in the liver and the lungs. During the course of his therapy, the patient's serum alpha-fetoprotein levels and serum lipase levels rose concurrently, suggesting tumor-associated production of both of these factors. Seventeen months after the diagnosis of metastatic pancreatoblastoma, the patient died from his disease. Our case illustrates the fact that pancreatoblastomas are extremely difficult to diagnosis preoperatively. In addition, our case demonstrates that pancreatoblastomas can be alpha-fetoprotein producing, hormone producing, and enzyme producing when it occurs in adults.

Genome-wide allelotyping of a new in vitro model system reveals early events in breast cancer progression.

Toward the goal of identifying early genetic losses, which mediate the release of human breast epithelium from replicative suppression leading to cellular immortalization, we have used a newly developed in vitro model system. This system consists of epithelial cultures derived from noncancerous breast tissue, treated with the chemical carcinogen N-ethyl-N-nitrosourea, and continuously passaged to yield cell populations culminating in the immortal phenotype. Genome-wide allelotyping of early passage N-ethyl-N-nitrosourea-exposed cell populations revealed aberrations at >10% (18 of 169) loci examined. Allelic losses encompassing chromosomes 6q24-6q27, implicating immortalization-associated candidate genes, hZAC and SEN6, occurred in two independently derived cell lines before the Hayflick limit. Additional LOH sites were present in one cell line at 3p11-3p26, 11p15, and 20p12-13. Allelic losses reported in this cell line preceded detectable levels of telomerase activity and the occurrence of p53-related aberrations. Information gained from the search for early immortalization-associated genetic deletions in cultured cells was applied in a novel approach toward the analysis of morphologically normal terminal ductal lobular units microdissected from 20 cases of ductal carcinoma in situ. Notably, clonal allelic losses at chromosome 3p24 and 6q24 were an early occurrence in adjoining terminal ductal lobular units of a proportion of primary tumors, which displayed loss of heterozygosity (3 of 11 and 3 of 6, respectively). The biological insights provided by the new model system reported here strongly suggest that early allelic losses delineated in immortalized cultures and validated in vivo could serve as surrogate endpoints to assist in the identification and intervention of high-risk benign breast tissue, which sustains the potential for continuous proliferation.