Management of vagus nerve stimulation therapy in the peri-operative period: Guidelines from the Association of Anaesthetists: Guidelines from the Association of Anaesthetists.

Vagus nerve stimulation is a well-established treatment option for patients with drug-resistant epilepsy and has an expanding range of other clinical indications. Side effects of vagus nerve stimulation therapy include: cough; voice changes; vocal cord adduction; rarely, obstructive sleep apnoea; and arrhythmia. Patients with implanted vagus nerve stimulation devices may present for unrelated surgery and critical care to clinicians who are unfamiliar with their function and safe management. These guidelines have been formulated by multidisciplinary consensus based on case reports, case series and expert opinion to support clinicians in the management of patients with these devices. The aim is to provide specific guidance on the management of vagus nerve stimulation devices in the following scenarios: the peri-operative period; peripartum period; during critical illness; and in the MRI suite. Patients should be aware of the importance of carrying their personal vagus nerve stimulation device magnet with them at all times to facilitate urgent device deactivation if necessary. We advise that it is generally safer to formally deactivate vagus nerve stimulation devices before general and spinal anaesthesia. During periods of critical illness associated with haemodynamic instability, we also advise cessation of vagus nerve stimulation and early consultation with neurology services.

Influence of complications following immediate breast reconstruction on breast cancer recurrence rates.

BACKGROUND: The rate of immediate breast reconstruction is rising. Postoperative infections are more frequent in patients who undergo reconstruction. The inflammatory response to a postoperative infection can increase the risk of tumour recurrence in other forms of cancer through the release of proinflammatory mediators. The aim of this study was to assess the relationship between complications and breast cancer recurrence in patients undergoing immediate reconstruction. METHODS: This was a review of a prospectively maintained database of all patients who had immediate breast reconstruction between 2004 and 2009 at Galway University Hospital, a tertiary breast cancer referral centre serving the west of Ireland. All patients had a minimum follow-up of 5 years. Outcomes assessed included the development of wound complications and breast cancer recurrence. The data were evaluated by univariable and multivariable Cox regression analysis. RESULTS: A total of 229 patients who underwent immediate reconstruction were identified. The overall 5-year recurrence-free survival rate was 85·6 per cent. Fifty-three patients (23·1 per cent) had wound complications, of whom 44 (19·2 per cent) developed a wound infection. There was a significantly greater risk of developing systemic recurrence among patients who experienced a postoperative wound complication compared with those without a complication (hazard ratio 4·94, 95 per cent c.i. 2·72 to 8·95; P < 0·001). This remained significant after adjusting for Nottingham Prognostic Index group in the multivariable analysis. The 5-year recurrence-free survival rate for patients who had a wound complication was 64 per cent, compared with 89·2 per cent in patients without a complication (P < 0·001). CONCLUSION: This study has demonstrated that wound complications after immediate breast reconstructive surgery have significant implications for patients with breast cancer. Strategies are required to minimize the risk of postoperative wound complications in patients with breast cancer undergoing immediate reconstruction.

The h index and the identification of global benchmarks for breast cancer research output.

The h index is used to assess an individual's contribution to the literature. This metric should not be employed to compare individuals across research areas; rather each subject should have its own baseline and standard. This work aimed to identify global bibliometric benchmarks for those involved in breast cancer research, and specifically, to describe the bibliographic characteristics of breast surgeons in the UK and Ireland. Authorship data was extracted from breast cancer related output from 1945 to 2008, as indexed in the Web of Science. Authors' publications, citations and h indexes were identified. The breast-related output of 277 UK and Irish breast surgeons was evaluated, and a citation report generated for each. Strong correlation was noted between the h index and number of publications (r = 0.642, P < 0.001) and number of total citations (r = -0.922, P < 0.001). The author with the highest h index is B Fisher (h index = 80). 23.0% of surgeons had not published original research pertaining to the breast; the remainder had together produced 2,060 articles, accounting for 59,002 citations. The top quartile was responsible for 83% of output; the 90th percentile was 20 publications. The range of h index values for the surgeons was 0-50, with a median h index returned of 3 (IQR 1-6); the 90th percentile was 13.5. This work has identified bibliometric benchmarks to which those involved in breast cancer research might aspire. Our findings suggest that there is need for wider involvement of surgeons in the research process and raises questions regarding the future of scientific breast surgery.

NCCP breast cancer referral guidelines--are breast cancer patients prioritised?

Following centralisation of breast cancer services, the National Cancer Control Programme (NCCP) introduced referral guidelines indicating which patients require urgent, early and routine review. This study prospectively analysed referrals to a symptomatic breast unit over 3 months to measure Primary Care Physician (GP) uptake of the NCCP referral guidelines, compare triage patterns of GP and consultant breast surgeon and evaluate the efficacy of the guidelines at identifying patients with breast cancer. 1044 consecutive referrals were categorised according to NCCP guidelines. 637 (61%) were referred using the NCCP form. GP referrals correlated well with consultant breast surgeon for patients requiring urgent review (r = 0.71, p < 0.001; Pearson). Patients categorised as "urgent" were more likely to have a breast biopsy compared to those categorised as "routine" (p < 0.0001; Chi2). The overall cancer incidence was 34 (3.3%) and significantly higher in the "urgent" group at 10.5%. NCCP guidelines were 91% sensitive for triaging breast cancer patients into the correct (urgent) category. The NCCP guidelines are accurate and should be considered the gold-standard for referral to the symptomatic breast service. Consideration should be given to a GP-delivered service to patients outside the "urgent" category.

The impact of progesterone receptor negativity on oncological outcomes in oestrogen-receptor-positive breast cancer.

BACKGROUND: Oestrogen receptor (ER) status provides invaluable prognostic and therapeutic information in breast cancer (BC). When clinical decision making is driven by ER status, the value of progesterone receptor (PgR) status is less certain. The aim of this study was to describe clinicopathological features of ER-positive (ER+)/PgR-negative (PgR-) BC and to determine the effect of PgR negativity in ER+ disease. METHODS: Consecutive female patients with ER+ BC from a single institution were included. Factors associated with PgR- disease were assessed using binary logistic regression. Oncological outcome was assessed using Kaplan-Meier and Cox regression analysis. RESULTS: In total, 2660 patients were included with a mean(s.d.) age of 59.6(13.3) years (range 21-99 years). Median follow-up was 97.2 months (range 3.0-181.2). Some 2208 cases were PgR+ (83.0 per cent) and 452 were PgR- (17.0 per cent). Being postmenopausal (odds ratio (OR) 1.66, 95 per cent c.i. 1.25 to 2.20, P < 0.001), presenting with symptoms (OR 1.71, 95 per cent c.i. 1.30 to 2.25, P < 0.001), ductal subtype (OR 1.51, 95 per cent c.i. 1.17 to 1.97, P = 0.002) and grade 3 tumours (OR 2.20, 95 per cent c.i. 1.68 to 2.87, P < 0.001) were all associated with PgR negativity. In those receiving neoadjuvant chemotherapy (308 patients), pathological complete response rates were 10.1 per cent (25 of 247 patients) in patients with PgR+ disease versus 18.0 per cent in PgR- disease (11 of 61) (P = 0.050). PgR negativity independently predicted worse disease-free (hazard ratio (HR) 1.632, 95 per cent c.i. 1.209 to 2.204, P = 0.001) and overall survival (HR 1.774, 95 per cent c.i. 1.324 to 2.375, P < 0.001), as well as worse overall survival in ER+/HER2- disease (P = 0.004). CONCLUSIONS: In ER+ disease, PgR- tumours have more aggressive clinicopathological features and worse oncological outcomes. Neoadjuvant and adjuvant therapeutic strategies should be tailored according to PgR status.

Disease recurrence and oncological outcome of patients treated surgically with curative intent for estrogen receptor positive, lymph node negative breast cancer.

BACKGROUND: The molecular era has identified four breast cancer subtypes. Luminal A breast cancer (LABC) is defined by estrogen-receptor positive (ER+), progesterone-receptor positive (PgR+) and human epidermal growth factor receptor-2 negative (HER2-) tumours; these cancers are the most common and carry favourable prognoses. AIMS: To describe clinicopathologic features, oncological outcome and relapse patterns in LABC. METHODS: Consecutive female patients diagnosed with ER/PgR+/HER2-, lymph node negative (LN-) breast cancer between 2005 and 2015 were included. Clinicopathological and recurrence data was recorded using descriptive statistics. Oncological outcome was determined using Kaplan-Meier and Cox-regression analyses. RESULTS: Analysis was performed for 849 patients with median follow-up of 102.1 months. Mean disease-free (DFS) and overall survival (OS) were 85.8% and 91.8%. Seventy patients died during this study (8.2%), while 58 patients had recurrence; 7 had local recurrence (0.8%) and 51 had distant recurrence (DDR) (6.0%). Patients developing DDR were likely to be postmenopausal (P = 0.028), present symptomatically (P < 0.001) and have larger tumours (P < 0.001). The mean time to DDR was 65.7 months, with fatal recurrence occurring in 66.6% of patients with DDR (34/51). Systemic chemotherapy prescription did not influence DDR (P = 0.053). Age >65 (hazards ratio (HR):1.66, 95% Confidence Interval (CI):1.07-2.55, P = 0.022), presenting symptomatically (HR:2.28, 95%CI:1.21-4.29, P = 0.011) and tumour size >20 mm (HR:1.81, 95%CI:1.25-2.62, P = 0.002) predicted DFS, while age>65 (HR:2.60, 95%CI:1.49-4.53, P = 0.001) and being postmenopausal at diagnosis (HR:3.13, 95%CI:1.19-8.22, P = 0.020) predicted OS. CONCLUSION: Our series demonstrated excellent survival outcomes for patients diagnosed with LN- LABC after almost a decade of follow-up. However, following DDR, fatal progression is often imminent.

Authorship trends in the surgical literature.

BACKGROUND: Authorship is increasingly influential in career progression and academic promotion. This study aimed to examine authorship trends in surgical titles between 1998 and 2008, and to compare these trends with those in general medicine publications. METHODS: Clinical trials published in high-impact medical and surgical titles were identified. The number of authors associated with these studies and trends over time were analysed using PubReMiner. Trends were then compared between titles with and without author contribution forms (ACFs). Author numbers in top-cited articles were correlated with citation rates. RESULTS: Some 6290 trials involving 54,120 different authorships were identified. A significant difference was found between authorship numbers associated with clinical trials in medicine versus those in surgery (P = 0.003). Introduction of ACFs did not influence the number of authors per trial (P = 0.670). The top 100 most highly cited articles accounted for 114,935 citations; author number correlated with subsequent citation rate (r = 0.26, P = 0.011). CONCLUSION: Author numbers have increased in the past decade, in both medical and surgical journals. Although medical output is associated with significantly higher levels of authorship, the difference cannot be explained by complexity of research alone.

Does Mode of Surgical Intervention Based on Oncotype DX Score Influence Disease Recurrence in Early Breast Cancer?

Introduction Routine utilization of multigene assays to inform operative decision-making in early breast cancer (EBC) treatment is yet to be established. In this pilot study, we sought to establish the potential benefits of surgical intervention in EBC based on recurrence risk quantification using the Oncotype DX (ODX) assay. Materials and Methods Consecutive ODX tests performed over a 9-year period from October 2007 to May 2016 were evaluated. Oncotype scores were classified into high (≥31), medium (18-30), or low-risk (0-17) groups. The primary outcome was breast cancer recurrence. Subgroup analysis offered assessment of the recurrence effect of mode of surgical intervention for patient groups as defined by the oncotype score. Results In total 361 patients underwent ODX testing. The mean age and follow-up were 55.25 (± 10.58) years and 38.59 (± 29.1) months, respectively. The majority of patients underwent wide local excision (86.7%) with 8.9 and 4.4% patients having a mastectomy or wide local excision with completion mastectomy, respectively. Fifty-one percent of patients fell into the low risk ODX category with a further 40.2 and 8.5% deemed to be of intermediate and high risk. Five patients (1.38%) had disease recurrence. Comparative analysis of operative groups in each oncotype group revealed no difference in recurrence scores in the low- ( p = 0.84) and high-risk groups ( p = 0.92) with a statistically significant difference identified in the intermediate risk group ( p = 0.002). Conclusion To date we have been unable to definitively identify a role for ODX in guiding surgical approach in EBC. There is, however, a need for larger studies to examine this hypothesis.

Cyclical ischaemic preconditioning modulates the adaptive immune response in human limb ischaemia-reperfusion injury.

BACKGROUND: Reperfusion injury (RI) has significant local and systemic consequences. Ischaemic preconditioning (IPC) modulates RI and the innate immune response. This study examined whether IPC attenuates RI-mediated changes in lymphocyte populations and function following elective surgery. METHODS: Twenty-five patients sustaining 1 h of tourniquet ischaemia during cruciate ligament reconstruction were randomized before surgery to three 5-min ischaemia cycles separated by 5 min of reperfusion, or to a control group. Systemic levels of interleukin (IL) 4 and interferon (IFN) gamma, and surface expression of CD45ro/ra, CD62L and CD95 were measured. T cells were examined systemically and in stimulated serum co-culture to determine CD4/CD8 and Th1/Th2 shifts through intracellular cytokine production. RESULTS: CD4 CD45ro cell numbers increased after RI without IPC, whereas CD8 cells expressing CD45ro and CD95 increased with IPC. Preconditioned serum in co-culture attenuated increases in CD4 and decreases in CD8 numbers, a process prevented by inhibition of antigen activation. Following RI, systemic IL-2 levels were significantly lower after IPC, whereas co-culture with post-RI serum increased proinflammatory intracellular cytokine production. CONCLUSION: IPC modulated T cell responses in limb RI through reduced activation and proinflammatory cytokine production by CD4 cells, while preventing CD4/CD8 derangement. IPC prevented lymphocyte-directed immune dysfunction.

Re-Appraisal of Estrogen Receptor Negative/Progesterone Receptor Positive (ER-/PR+) Breast Cancer Phenotype: True Subtype or Technical Artefact?

Expression of the ER and PR receptors is routinely quantified in breast cancer as a predictive marker of response to hormonal therapy. Accurate determination of ER and PR status is critical to the optimal selection of patients for targeted therapy. The existence of an ER-/PR+ subtype is controversial, with debate centred on whether this represents a true phenotype or a technical artefact on immunohistochemistry (IHC). The aim of this study was to investigate the true incidence and clinico-pathological features of ER-/PR+ breast cancers in a tertiary referral symptomatic breast unit. Clinico-pathological data were collected on invasive breast cancers diagnosed between 1995 and 2005. IHC for ER and PR receptors was repeated on all cases which were ER-/PR+, with the same paraffin block used for the initial diagnostic testing. Concordance between the diagnostic and repeat IHC was determined using validated testing. Complete data, including ER and PR status were available for 697 patients diagnosed during the study period. On diagnostic IHC, the immunophenotype of the breast tumours was: ER+/PR+ in 396 (57%), ER-/PR- in 157 (23%), ER+/PR- in 88 (12%) and ER-/PR+ in 56 (8.6%) patients. On repeat IHC of 48/56 ER-/PR+ tumours 45.8% were ER+/PR+, 6% were ER+/PR- and 43.7% were ER-/PR- None of the cases were confirmed to be ER-/PR+. The ER-/PR+ phenotypic breast cancer is likely to be the result of technical artefact. Prompt reassessment of patients originally assigned to this subtype who re-present with symptoms should be considered to ensure appropriate clinical management.

Growth factor, steroid, and steroid antagonist regulation of cyclin gene expression associated with changes in T-47D human breast cancer cell cycle progression.

Cyclins and proto-oncogenes including c-myc have been implicated in eukaryotic cell cycle control. The role of cyclins in steroidal regulation of cell proliferation is unknown, but a role for c-myc has been suggested. This study investigated the relationship between regulation of T-47D breast cancer cell cycle progression, particularly by steroids and their antagonists, and changes in the levels of expression of these genes. Sequential induction of cyclins D1 (early G1 phase), D3, E, A (late G1-early S phase), and B1 (G2 phase) was observed following insulin stimulation of cell cycle progression in serum-free medium. Transient acceleration of G1-phase cells by progestin was also accompanied by rapid induction of cyclin D1, apparent within 2 h. This early induction of cyclin D1 and the ability of delayed administration of antiprogestin to antagonize progestin-induced increases in both cyclin D1 mRNA and the proportion of cells in S phase support a central role for cyclin D1 in mediating the mitogenic response in T-47D cells. Compatible with this hypothesis, antiestrogen treatment reduced the expression of cyclin D1 approximately 8 h before changes in cell cycle phase distribution accompanying growth inhibition. In the absence of progestin, antiprogestin treatment inhibited T-47D cell cycle progression but in contrast did not decrease cyclin D1 expression. Thus, changes in cyclin D1 gene expression are often, but not invariably, associated with changes in the rate of T-47D breast cancer cell cycle progression. However, both antiestrogen and antiprogestin depleted c-myc mRNA by > 80% within 2 h. These data suggest the involvement of both cyclin D1 and c-myc in the steroidal control of breast cancer cell cycle progression.

Justifying adjuvant chemotherapy in breast cancer: a survey of women and healthcare professionals.

AIM: The absolute survival gains required to make adjuvant chemotherapy acceptable to women are unknown. We questioned women and healthcare professionals on the absolute survival benefits required to make adjuvant chemotherapy acceptable. METHODS: A cohort of 1000 Irish women and 402 UK nurses and surgeons were invited to choose an absolute survival advantage sufficient to justify adjuvant cytotoxic chemotherapy. The non-physician cohort included women with a history of cancer, female medical healthcare professionals and women with no personal or professional experience of cancer. RESULTS: Eight hundred and thirty-five women completed the questionnaire; 769, 651 and 413 said they would accept chemotherapy for a 10%, 5% and 1% survival advantage, respectively. There was a significant difference in women's preferences depending on their personal and professional experience of cancer. Eighty-nine women had personal experience of chemotherapy and these women were more likely to accept chemotherapy for any survival advantage (88, 87 and 66 for a 10%, 5% and 1% survival advantage, respectively; p=0.0023; Chi(2)). Surgeons and nurses were less likely to accept chemotherapy for smaller absolute survival advantages. CONCLUSIONS: This study confirms that women require modest absolute gains to choose adjuvant chemotherapy. The pattern of acceptance differs significantly between those with professional experience of cancer, a personal history of chemotherapy use and a history of cancer or not.

A comparison of surgical impression, histological findings and microbiological results at open appendicectomy.

There is no accurate predictor of complications following open appendicectomy. Surgical impression, histological findings and peritoneal culture swabs have been used. The value of peritoneal culture swab was assessed in this study. All patients undergoing open appendicectomy between January 2003 and December 2005 were included in the study. During the 24-month period, 952 patients underwent open appendicectomy. Peritoneal culture swabs were taken from 309 patients (32%). There was a significant difference in the mean postoperative length of stay +/- SEM between those with a positive culture (7 days +/- 0.6), those with a sterile culture result (3.7 days +/- 0.2) and those on whom a culture swab was not taken (4.9 days +/- 0.3); p<0.0001, ANOVA. Surgeons were more likely to overcall the severity of the appendix pathology (p < 0.0001 surgical vs. histological findings; Fisher's exact test), however, there was no significant difference in the power of surgical or histological assessment of the appendicitis at predicting a positive peritoneal culture result. Complex appendicitis was more likely to be associated with a positive peritoneal culture (P < 0.0001; Fisher's exact test). No antibiotic regime was changed on the basis of a positive culture swab. Fifteen patients were readmitted within 6 months of appendicectomy, predictors of readmission included histologically confirmed complex appendicitis and a positive peritoneal culture swab. Peritoneal culture swabs do not improve immediate postoperative therapy based on surgical impression and rapid histological reporting, however, the routine use of peritoneal culture swabs may be of value in identifying patients requiring outpatient follow-up.

The clinical and pathological differences in prevalent round screen-detected and symptomatic invasive breast cancer.

The potential benefits of breast cancer screening include the detection of cancers at a more favourable stage, however, cancers detected during the prevalent round of screening may differ from true screen-detected cancers. These differences are poorly defined. This study prospectively assessed all women between 50 and 64 years of age undergoing curative surgery for breast cancer, both screen-detected and symptomatic, in one screening centre during the prevalent round of the national breast cancer-screening programme. Four hundred and thirty seven patients (364 screen-detected and 73 symptomatic patients) underwent surgery for breast cancer. Symptomatic breast cancers were of a higher grade (p < 0.0001; Chi2) and less likely to be oestrogen receptor positive (49% versus 88%; p < 0.0001; Fisher's exact test); however there was no difference in size of tumour or axillary nodal positivity. This study suggests that tumours detected by screening during the prevalent round of a screening programme are of a more prognostically favourable type than symptomatic breast cancers in the same age group.

Surgical management of perforated peptic ulcer disease.

BACKGROUND: Surgery for perforated peptic ulcer disease is one of the most common emergency procedures carried out in the western world. The role of postoperative empiric Helicobacter Pylori eradication therapy is controversial. METHODS: The clinical, operative and postoperative surveillance details of 84 consecutive patients who underwent surgery for perforated peptic ulcer were reviewed. RESULTS: All patients underwent omentopexy +/- simple closure followed by proton pump therapy. Patients were followed-up for an average of 44 +/- 19 months. Females were older than male patients (59 +/- 20 vs. 46 + 17 years; p<0.05), presented with symptoms of a longer duration (17.9 +/- 16 vs. 8.9 +/- 9 hours; p=0.045) and had a higher mortality rate (18% vs 3%; p<0.05). Seventy-nine per cent of patients received postoperative empiric Helicobacter Pylori eradication therapy. CONCLUSIONS: Surgery for perforated peptic ulcer is associated with a significant perioperative mortality rate. Elderly female patients are particularly at risk.

A qualitative analysis of the attitudes of Irish patients towards participation in genetic-based research.

BACKGROUND: Progress in diagnostic and therapeutic strategies in medicine is dependent upon high-quality biomedical research. Technological advances have facilitated improved understanding of disease aetiology, and rapidly emerging data promises further progress. Translating this potential into the clinic depends on patient participation in innovative clinical trials. We investigated attitudes to genetic research in Ireland, particularly with respect to commercial and financial implications. METHODS: A multi-centre, cross-sectional survey study was performed. Consecutive out-patients attending four clinics were asked to complete paper-based questionnaires. The same questionnaire was publicly available in electronic format on www.surveymonkey.com for 72 h. Data were analysed using SPSS. RESULTS: 351 questionnaires were completed (99 paper, 252 electronic). The majority of respondents were female (n = 288, 82 %), and highly educated, with 244 (70 %) attending college/university. Most participants supported genetic research (267, 76 %), more frequently for common diseases (274, 78 %) than rare disorders (204, 58 %, p < 0.001, χ 2). 103 (29 %) had participated in scientific research, and 57 (16 %) had donated material to a bio-bank. The majority (n = 213, 61 %) would not support research with potential financial/commercial gain. 106 (30 %) would decline to participate in research if researchers would benefit financially, compared to 49 (14 %) if the research was supported by a pharmaceutical company (p < 0.001, χ 2). Respondents would provide buccal samples (258, 74 %) more readily than tissue (225, 64 %) or blood (222, 63 %). CONCLUSIONS: A high level of support for genetic research exists among the Irish population, but active participation is dependent upon a number of factors, notably, type of biological material required, frequency of the disease in question, and commercial interest of the researchers.

Cyclin D2 activates Cdk2 in preference to Cdk4 in human breast epithelial cells.

To investigate the possibility of differing roles for cyclins D1 and D2 in breast epithelial cells, we examined the expression, cell cycle regulation and activity of these two G1 cyclins in both 184 normal breast epithelial cells and T-47D breast cancer cells. Synchronisation studies in 184 cells demonstrated that cyclin D1 and cyclin D2 were differentially regulated during G1, with cyclin D2 abundance increasing by 3.7-fold but only small changes in cyclin D1 abundance observed. The functional consequences of increased cyclin D2 expression were examined in T-47D cells, which express no detectable cyclin D2. Induced expression of cyclin D2 resulted in increases in cyclin E expression, pRB phosphorylation and the percentage of cells in S-phase, while constitutive expression resulted in a consistent trend toward reduced dependence on serum for continued proliferation. Thus, cyclin D2 is a positive regulator of G1 progression in breast cells analogous to the well-documented effects of cyclin D1. Indeed, equimolar concentrations of inducible cyclin D1 and D2 resulted in quantitatively similar cell cycle effects. Marked divergence was found, however, in the CDKs activated by the two cyclins in breast epithelial cells. Cyclin D2 complexes contained a higher Cdk2/Cdk4 ratio than cyclin D1 complexes. The cyclin D2-associated kinase activity was largely inhibited by Cdk2-specific inhibitors and could phosphorylate histone H1, a substrate for Cdk2 but not for Cdk4 and Cdk6. Therefore, cyclin D2 preferentially activated Cdk2 in breast epithelial cells. In contrast, Cdk4 and Cdk6 were predominantly responsible for cyclin D1-associated kinase activity as previously reported. Thus, although cyclins D1 and D2 elicited similar effects on breast epithelial cell cycle progression they appeared to achieve this end via activation of different CDKs. This is the first evidence of cyclin D2 activating Cdk2 in mammalian cells thus providing further evidence that D-type cyclins are not necessarily redundant.

Lack of relationship between CDK activity and G1 cyclin expression in breast cancer cells.

The G1 cyclins, cyclin D1 and E, are rate limiting for progression through G1 phase of the cell cycle in breast epithelial cells and are oncogenic when expressed in the mammary epithelium of transgenic mice. These genes are frequently overexpressed in clinical breast cancer where overexpression appears to be associated with specific disease phenotypes, altered responsiveness to therapeutic intervention and patient survival. In order to investigate the functional correlates of cyclin D1 and cyclin E overexpression we employed a panel of normal, immortalized and neoplastic breast epithelial cell lines to examine the relationships between cyclin gene expression, cyclin-CDK complex formation and CDK activity. In agreement with earlier studies cyclin D1 and E expression varied over an approximately tenfold range among the 18 cell lines studied. There was no apparent relationship, however, between cyclin D1 expression and the in vitro activity of its major kinase partner, Cdk4, although MDA-MB-134 cells displayed the highest level of both cyclin D1 expression and Cdk4 activity. Similarly, there was no significant relationship between cyclin E expression and cyclin E-Cdk2 activity. Fractionation of whole cell lysates by gel filtration chromatography revealed that approximately 90% of the cyclin E protein was present in inactive complexes containing the CDK inhibitors p21 and p27. Much of the small fraction of active cyclin E protein was of very high apparent molecular mass, >400 kDa, suggesting that formation of these complexes is a more important determinant of cyclin E-Cdk2 activity than cyclin E abundance. These data suggest that properties of cyclins D1 and E in addition to their ability to activate Cdk4 and Cdk2 may contribute to the effects of overexpression on the breast cancer phenotype.