Peter A Learn

San Antonio Military Medical Center, Texas City, Texas, United States

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Publications (12)42.26 Total impact

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    ABSTRACT: Despite improved clinical characterization, autoimmune pancreatitis is often still diagnosed only after a major operative procedure. This study seeks to elucidate the circumstances that contribute to an inaccurate preoperative diagnosis. Two independent reviewers identified retrospectively an institutional cohort of 68 patients with adequate clinical data to support the diagnosis of autoimmune pancreatitis. Further data regarding presentation, diagnostic studies, and clinical course was abstracted from medical records. Comparative analyses were performed between those patients who underwent major operative procedures and those who did not. Fifty-three patients underwent operative intervention as their initial treatment. Compared to the 15 patients avoiding operation, these patients were less likely to have diffuse pancreatic enlargement identified on pretreatment imaging (8% vs 80%) or to have pretreatment serum IgG4 level evaluations (11% vs 100%). Among the 21 patients in whom IgG4 levels were first checked postoperatively, only 12 had increases of at least twice the upper limit of normal. Pretreatment fine needle aspirates were interpreted incorrectly as definite or suspicious for adenocarcinoma in 12 patients, of whom 10 underwent operation. Clinically important postoperative disease recurrence was suspected or proven in 13 patients. Pitfalls leading to major pancreatic resections in autoimmune pancreatitis include unnecessarily high thresholds for initiating serum IgG4 evaluation, false positive cytologic evaluations for malignancy, and failure to recognize non-classic initial presentations, or recurrence of disease. Better diagnostic strategies are needed, but awareness of these specific findings should help to decrease the number of patients undergoing operation for unrecognized autoimmune pancreatitis.
    Surgery 09/2011; 150(5):968-74. · 3.37 Impact Factor
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    ABSTRACT: Schwannomas are usually benign nerve sheath tumors, which typically arise in the head, neck, spinal cord and extremities. Schwannoma of the biliary tract is an extremely rare finding. Patients generally lack symptoms and seek medical attention when tumor growth causes obstructive jaundice. Preoperative diagnosis is difficult and resection is the treatment of choice. A 54 year-old female with history of back and right labia minor melanoma for which she underwent complete excision and right inguinal lymph node dissection more than 10 years ago, was evaluated for new onset gastroesophageal reflux symptoms and found to have markedly abnormal liver enzymes. Imagining studies revealed intrahepatic ductal dilatation and a 5.2 cm mass in the porta hepatis that was not consistent with cholangiocarcinoma or hepatocellular carcinoma. Multiple percutaneous biopsies of the mass failed to provide a definitive diagnosis. With a high clinical suspicion of metastatic melanoma and no other evident sites of disease, operative intervention was undertaken for diagnosis and definitive treatment. Diagnostic laparoscopy was performed initially, but access to the mass was difficult, given its location. Subsequently, the patient underwent laparotomy, with tumor excision, common bile duct resection and hepato-jejunostomy. Pathologic examination and analysis were consistent with cellular schwannoma. Postoperatively, the patient recovered uneventfully, and liver function studies returned to normal. Schwannomas are uncommon tumors, which very rarely arise from the biliary tract and cause biliary obstruction. Exploration is indicated in order to establish the diagnosis and to render definitive treatment.
    Surgical Oncology 06/2011; 20(4):e157-9. · 2.14 Impact Factor
  • Peter A Learn, Peter B Bach
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    ABSTRACT: For more than a decade, health policy groups have recommended concentrating care for certain high-risk oncologic procedures into high-volume centers. The degree to which practice patterns and outcomes have changed over that time period is unclear. To evaluate temporal trends in the mortality and concentration of high-risk oncologic procedures. Retrospective cohort study using data from the Nationwide Inpatient Sample on 93,108 adult patients undergoing pancreatectomy, esophagectomy, gastrectomy, or major lung resection for organ-specific cancers from 1997 to 2006. The main outcome measure was in-hospital mortality. Risk- and volume-adjusted mortality decreased over time for all 4 procedures (P < 0.05). When hospitals were categorized into terciles of case volume, mortality gaps persisted between high- and low-volume centers in all procedures throughout the study period and did not significantly narrow over time. Patient volumes shifted toward high-volume centers over time for all procedures (P <0.001), although at the end of the study period, low-volume centers still cared for one-quarter to one-third of patients undergoing each of the studied procedures. Most of the overall improvements in mortality were attributable to decreasing mortality within volume categories as opposed to the effects of care concentration. Modest concentration into higher-volume centers has taken place over the past decade, but improvements within volume categories have driven most of the generalized decreases in mortality. Significant outcome gaps between high- and low-volume centers still persist; further centralization may retain the potential to lower overall mortality.
    Medical care 10/2010; 48(12):1041-9. · 3.24 Impact Factor
  • Peter A Learn, Peter B Bach
    Journal of thoracic oncology: official publication of the International Association for the Study of Lung Cancer 08/2010; 5(8):1111-2. · 4.55 Impact Factor
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    ABSTRACT: Gastrointestinal (GI) stromal tumor (GIST) is the most common mesenchymal tumor of the GI tract, constituting 80% of all GI mesenchymal tumors and approximately 20% of all small bowel malignancies, excluding lymphomas. This article provides a summary of recent randomized clinical trials of these tumors.
    Surgical Oncology Clinics of North America 01/2010; 19(1):101-13. · 1.22 Impact Factor
  • Gastroenterology 01/2010; 138(5). · 12.82 Impact Factor
  • Peter A Learn, Morton S Kahlenberg
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    ABSTRACT: The expanding understanding of the genetic basis to hereditary colon cancer syndromes is dismantling previously conceived categorizations and shedding light on why those schemes often failed in past. This review highlights evolving concepts regarding the genetic diagnosis and clinical management of the more commonly inherited colorectal cancer syndromes, including a discussion of recently described familial syndromes. This review also addresses clinician responsibilities in recognition of familial syndromes and provision of counseling.
    Surgical Oncology Clinics of North America 02/2009; 18(1):121-44, ix. · 1.22 Impact Factor
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    ABSTRACT: A relationship between hospital procedural volume and patient outcomes has been observed in gastrectomies for primary gastric cancer, but modifiable factors influencing this relationship are not well elaborated. We performed a population-based study of 1864 patients undergoing gastrectomy for primary gastric cancers at 214 hospitals. Hospitals were stratified as high-, intermediate-, or low-volume centers. Multivariate models were constructed to evaluate the effect of institutional procedural volume and other hospital- and patient-specific factors on the risk of in-hospital mortality, adverse events, and failure to rescue, defined as mortality after an adverse event. High-volume centers attained an in-hospital mortality rate of 1.0% and failure-to-rescue rate of .7%, both less than one-fifth of that seen at intermediate- and low-volume centers, although adverse event rates were similar across the three volume tiers. In multivariate modeling, treatment at a high-volume hospital decreased the odds of mortality (odds ratio [OR], .22; 95% confidence interval [95% CI], .05-.89), whereas treatment at an institution with a high ratio of licensed vocational nurses per bed increased the odds of mortality (OR, 1.96; 95% CI, 1.04-3.75). Being treated at a hospital with a greater than median number of critical care beds decreased odds of mortality (OR, .46; 95% CI, .25-.81) and failure to rescue (OR, .53; 95% CI, .29-.97). Undergoing gastrectomy at a high-volume center is associated with lower in-hospital mortality. However, improving the rates of mortality after adverse events and reevaluating nurse staffing ratios may provide avenues by which lower-volume centers can improve mortality rates.
    Annals of Surgical Oncology 07/2007; 14(6):1846-52. · 4.12 Impact Factor
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    ABSTRACT: Tyrosine kinase receptors of the ErbB family have become promising targets for anti-neoplastic drugs, but mechanisms of resistance are incompletely understood. To investigate such pathways, we applied a small-molecule, selective EGFR inhibitor, OSI-774, to three well-characterized colon cancer cell lines and studied the alterations of expression and activation of receptors in the erbB family. MTT assays were performed to determine the IC(50)s of GEO, FET, and HCT 116 human colorectal cancer cell lines treated with OSI-774. Plated cells were then exposed to either DMSO control or 7 microm of OSI-774 for treatment durations of 1, 3, 5, 7, 10, 14, 28, and 56 days. Cell lysates were evaluated by Western blotting, evaluating both total and phosphorylated levels of EGFR, Her-2/neu, and erbB-3. IC(50) values for GEO, FET, and HCT 116 cell lines exposed to OSI-774 were 12.0, 16.0, and greater than 100 microm, respectively. In all treated cell lines, OSI-774 diminished EGFR activation but did not affect total expression compared with controls. In contrast, Her-2/neu activation was increased in all cell lines. These changes in EGFR and Her-2/neu were identified within 24 h but peaked later in the treatment cycle. ErbB-3 expression and activation did not follow a consistent pattern between cell lines. Inhibition of EGFR led to increased activation of Her-2/neu. This result suggests a possible mechanism by which cells might escape the proapoptotic signals resulting from EGFR blockade. Our findings suggest concurrent inhibition of multiple members of the erbB family may yield stronger apoptotic responses than single receptor blockade alone.
    Journal of Surgical Research 01/2007; 136(2):227-31. · 2.02 Impact Factor
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    ABSTRACT: Laparoscopic hepatic resection has been reported to yield lower morbidity and shorter hospital stays than open resection. However, few studies have evaluated patient and technical factors associated with short hospital stays. We conducted a retrospective review of patients undergoing laparoscopic hepatic resection at our institution from May 2002 to February 2004. Patient and operative factors were analyzed with respect to time to discharge. Seventeen patients underwent 10 wedge resections and seven segmentectomies or bisegmentectomies. There were no mortalities, conversions to open procedure, clinically evident bile leaks, or transfusion requirements. Eleven patients were discharged within 24 hours. When compared with those discharged later than 24 hours, there were fewer patients with advanced ASA classification (0 versus 3 in ASA class 3, p < 0.05). With appropriate patient selection, laparoscopic hepatic resections may be safely performed, result in short hospital stays, and are facilitated by technologies such as saline-enhanced electrocautery and endoscopic ultrasound. Information reflected in advanced ASA class may predict patients unlikely to be discharged within 24 hours.
    Journal of Gastrointestinal Surgery 04/2006; 10(3):422-7. · 2.36 Impact Factor
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    ABSTRACT: BACKGROUND The use of biologic markers to predict response to neoadjuvant chemotherapy may permit tailoring regimens to achieve maximal tumor response. Taxanes have demonstrated excellent activity in breast carcinoma; however, tumor-specific factors that predict clinical response have not been characterized thoroughly.METHODS The authors performed a historic review evaluating the association of tumor prognostic factors and response to neoadjuvant cyclophosphamide and doxorubicin (AC) with or without docetaxel (D) (AC vs. AC+D) in 121 women who previously were enrolled in a Phase III, randomized, clinical trial. Using pretreatment biopsy materials, immunohistochemical studies were performed for estrogen receptor (ER), progesterone receptor (PR), HER-2/neu, p53, and Ki-67. Outcome variables were pathologic complete response (pCR) and positive clinical response (cPOS), which was defined as a ≥ 50% regression in clinical tumor size prior to surgery.RESULTSIn a multivariate analysis that controlled for tumor size and lymph node status, improved cPOS rates were observed with the addition of docetaxel in women with HER-2/neu-negative tumors (81% vs. 51%; P < 0.05), yielding an adjusted odds ratio of 3.5 (95% confidence interval, 1.2–13.0) in favor of docetaxel. Women who had HER-2/neu-negative tumors appeared to have a lower response rate with AC alone compared with women who had HER-2/neu-positive tumors (51% vs. 75%; P = 0.06), but response rates were matched when docetaxel was added (81% vs. 78%; P = 0.99). ER, PR, p53, and Ki-67 results were not associated significantly with response rates.CONCLUSIONSHER-2/neu status may predict improved clinical response rates from the addition of docetaxel to anthracycline-based neoadjuvant chemotherapy. Docetaxel may “rescue” the response in women who have HER-2/neu-negative tumors to match that observed in women who have HER-2/neu-positive tumors treated with AC alone. Cancer 2005. © 2005 American Cancer Society.
    Cancer 05/2005; 103(11):2252 - 2260. · 5.20 Impact Factor
  • Current Surgery 01/2005; 62(2):204-7.

Publication Stats

106 Citations
42.26 Total Impact Points

Institutions

  • 2011
    • San Antonio Military Medical Center
      Texas City, Texas, United States
  • 2010
    • Memorial Sloan-Kettering Cancer Center
      • Department of Surgery
      New York City, NY, United States
  • 2009
    • University of Texas Health Science Center at San Antonio
      • Department of Surgery
      San Antonio, TX, United States
  • 2005–2006
    • Wilford Hall Ambulatory Surgery Center
      Lackland Air Force Base, Texas, United States