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Corresponding author at: Regional Centre for Excellence in Palliative Care, Department of Oncology, Oslo University Hospital, Ullevål, Box 4956, Nydalen, 0424 Oslo, Norway. Tel.: +47 23 02 68 28; fax: +47 22 11 80 75.
Regional Centre for Excellence in Palliative Care, Oslo University Hospital, Oslo, NorwayEuropean Palliative Care Research Centre, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway
Oral Medicine Clinic, Department of Oral and Maxillofacial Surgery, Chaim Sheba Medical Center, Tel-Hashomer, IsraelDepartment of Oral Pathology and Oral Medicine, School of Dental Medicine, Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel
Department of Oral Surgery and Oral Medicine, Faculty of Dentistry, University of Oslo, NorwayDepartment of Maxillofacial Surgery and Hospital Odontology, Oslo University Hospital, Oslo, Norway
Assessment of oral and dental problems is seldom routine in clinical oncology, despite the potential negative impact of these problems on nutritional status, social function and quality of life (QoL). The aim was to develop a supplementary module to the European Organisation for Research and Treatment of Cancer Core Questionnaire (EORTC QLQ-C30) focusing on oral health and related QoL issues in all cancer diagnoses.
Methods
The module development followed the EORTC guidelines. Phases 1&2 were conducted in France, Germany, Greece, Netherlands, Norway and United Kingdom, while seven countries representing seven languages were included in Phase 3.
Results
Eighty-five QoL-items were identified from systematic literature searches. Semi-structured interviews with health-care professionals experienced in oncology and oral/dental care (n = 18) and patients (n = 133) resulted in a provisional module with 41 items. In phase 3 this was further tested in 178 European patients representing different phases of disease and treatment. Results from the interviews, clinical experiences and statistical analyses resulted in the EORTC QLQ-OH17. The module consists of 17 items conceptualised into four multi-item scales (pain/discomfort, xerostomia, eating, information) and three single items related to use of dentures and future worries.
Conclusion
This study provides a useful tool intended for use in conjunction with the EORTC QLQ-C30 for assessment of oral and dental problems. The increased awareness may lead to proper interventions, thereby preventing more serious problems and negative impact on QoL. The reliability and validity, the cross-cultural applicability and the psychometric properties of the module will be tested in a larger international study.
Today about 50% of patients with malignant diseases are cured, while the remaining 50% will live with their disease for shorter or longer periods of time.
oral complications are often insufficiently documented in patients with cancers outside this region, with potential for inadequate management of symptoms and negative impact on quality of life (QoL).
Lately, reports indicate an increasing incidence (up to 12%) of osteonecrosis of the jaw (ONJ), primarily due to treatment with bisphosphonates or targeted therapies.
A Norwegian descriptive study including a clinical oral examination in 99 palliative care cancer patients revealed that xerostomia was reported by 78% and that one-third had clinical oral candidiasis.
Sixty-seven percent reported mouth pain and 77% said they had received no information about oral side effects from treatment. Oral health may be defined as ‘A standard of health of the oral and related tissues which enables an individual to eat, speak and socialise without active disease, discomfort or embarrassment and which contributes to general well-being’.
including pain, social withdrawal and nutritional problems. It may be dose-limiting and consequently compromise prognosis. Thus, systematic assessment of oral health problems should be conducted regularly before, during and after treatment, in order to optimise treatment and symptom relief.
The European Organization for Research and Treatment of Cancer QLQ-C30: a quality-of-life instrument for use in international clinical trials in oncology.
is an extensively used QoL instrument in cancer clinical trials, supplemented by modules specifically focusing on QoL issues related to particular disease sites, symptoms and/or treatment-related issues. Neither the EORTC QLQ-C30,
The European Organization for Research and Treatment of Cancer QLQ-C30: a quality-of-life instrument for use in international clinical trials in oncology.
include specific questions regarding oral health problems, including oral pain and discomfort, xerostomia, problems with chewing, swallowing and social impact, that can be found in some QoL tools for H&N cancer.
The performance status scale for head and neck cancer patients and the functional assessment of cancer therapy-head and neck scale. A study of utility and validity.
Matched case-control study of quality of life and xerostomia after intensity-modulated radiotherapy or standard radiotherapy for head-and-neck cancer: initial report.
Development of a European Organization for Research and Treatment of Cancer (EORTC) questionnaire module to be used in quality of life assessments in head and neck patients.
Clinical and research collaboration between oral surgeons, dentists, oncologists and nurses at the Oslo University Hospital and Faculty of Dentistry, University of Oslo, Norway has identified the need for a brief assessment tool focusing on oral health problems and QoL to increase the awareness of these issues in clinical cancer care. Study objective was to develop a questionnaire supplemental to the EORTC QLQ-C30,
The European Organization for Research and Treatment of Cancer QLQ-C30: a quality-of-life instrument for use in international clinical trials in oncology.
Johnson C, Aaronson N, Blazeby J, Bottomley A, Fayers P, Koller M, et al. Guidelines for developing Questionnaire modules. Report 4th Ed. Brussels, 2011.
a process that consists of four phases, depicted in Table 1. This stepwise iterative work, including the evaluation by patients and health care professionals (HCP) at various steps is followed to ensure sufficient validity and reliability, clarity and comparability across languages and cultures. Phase 4 of the module development process consists of psychometric testing that will be carried out in a future study and not included here.
Table 1Development guidelines for European Organisation for Research and Treatment of Cancer (EORTC) disease or symptom-specific quality of life (QoL) modules.
Phase
Aim
Method
1
Generation of QoL issues relevant to the selected group of patients
1.
Literature search, review of all questionnaires related to oral and dental health
2.
Semi-structured interviews with health-care professionals and patients
3.
Analysis of qualitative and quantitative data
4.
Combination of results from interviews and analyses to produce a list of issues
2
Construction of a provisional questionnaire
1.
Consultation of the EORTC QoL group item database
2.
Construction of new items, and formatting of items according to EORTC format
3.
Translation of provisional questionnaire
3
Testing the questionnaire for relevance and acceptability
1.
Patients complete the EORTC QLQ-C30 and the module followed by interview
2.
Analysis of quantitative and qualitative data
3.
Modification of questionnaire
4.
Formal development report reviewed by EORTC QoL group
4
International field testing
Psychometric testing of the reliability, validity and sensitivity of the module in large international samples
2.1.1 Phase 1: Generation of relevant issues for oral health and QoL
Relevant issues/themes related to oral health and QoL in cancer were identified by extensive literature searches in the Medline/Ovid databases employing the MeSH terms: ‘oral health’, ‘cancer/neoplasm’, ‘quality of life’, ‘oral morbidity’, in all combinations, supplemented by searches in relevant textbooks. The following limitations applied: publication date: 1985–2007, adults and English language. Case reports, letters and editorials were excluded.
All abstracts were read, the full-text paper was retrieved if focussing on oral health in cancer and manual hand searching of all reference lists was conducted. All phase 3 or 4 EORTC modules were examined for relevant issues, as were other symptoms and QoL measures in general cancer/H&N cancer and specific inventories for dental/oral health problems.
The performance status scale for head and neck cancer patients and the functional assessment of cancer therapy-head and neck scale. A study of utility and validity.
Matched case-control study of quality of life and xerostomia after intensity-modulated radiotherapy or standard radiotherapy for head-and-neck cancer: initial report.
Development of a European Organization for Research and Treatment of Cancer (EORTC) questionnaire module to be used in quality of life assessments in head and neck patients.
The resulting list of issues was presented to experienced oncology HCPs from four countries. The relevance, frequency and severity of each issue were assessed by semi-structured interviews. The HCPs were asked to rate the issues from 1; ‘not relevant’ to 4; ‘very relevant’, to prioritise 5–10 issues and to add missing issues if any. The list was then presented to patients from six European cancer hospitals, who were interviewed and asked to indicate whether they perceived the issues as relevant, using the same categorical scale as the HCPs. They were asked to prioritise 5–10 issues for inclusion, to add issues that were not on the list and to provide comments.
2.1.2 Phase 2: Construction of the provisional questionnaire
Issues that were retained after Phase 1 were formatted into the conventional EORTC style with the response categories; 1; ‘not at all’, 2; ‘a little’, 3; ‘quite a bit’ and 4; ‘very much’ using a 1-week time frame if relevant. The EORTC QOL Item Bank
was consulted to ensure a uniform wording of items of identical symptoms across modules. Translations (Dutch, French, German, Greek, Hebrew, Norwegian and Swedish) were conducted according to EORTC procedures. Patient interviews (5–10) were performed in each language to detect translation errors.
2.1.3 Phase 3: Testing of the provisional questionnaire for relevance and acceptability
Phase 3 aims to identify problems related to the conceptualisation and clarity of items, to identify the need for new items or to delete redundant or confusing items. The preliminary module was therefore tested in another patient sample from the participating countries (except France) supplemented by Sweden and Israel. The inclusion of non-English speaking countries is crucial to determine the cross-cultural comparability of the module.
These patients were asked to complete both the EORTC QLQ-C30
The European Organization for Research and Treatment of Cancer QLQ-C30: a quality-of-life instrument for use in international clinical trials in oncology.
and the module followed by a semi-structured interview focusing on wording and conceptualisation. If items were perceived as annoying, confusing, upsetting or intrusive, patients were encouraged to suggest a better way of phrasing the question. They were also asked to delete irrelevant questions, add missing issues and to select the 5–10 most important issues.
2.2 Subjects
An inclusion matrix was used to ensure a wide distribution of diagnoses, treatment phases and socio-demographics. Eligibility criteria included patients with heterogeneous cancer diagnoses who understood and spoke the local language; ⩾18 years; who gave written informed consent and who were in active treatment or up to 3 years post-treatment. To ensure relevance of the module also for H&N cancer patients, and for palliative care patients (except in the final weeks), these groups were also included. Ethics Committee permissions were obtained according to local requirements.
2.3 Data analyses and criteria for item selection
The results from Phase 1 and 3 interviews were analysed using descriptive statistics, according to the EORTC guidelines at the time.
Johnson C, Aaronson N, Blazeby J, Bottomley A, Fayers P, Koller M, et al. Guidelines for developing Questionnaire modules. Report 4th Ed. Brussels, 2011.
Phase 1 items were retained if three of five criteria were fulfilled: mean score at least 1.5, prevalence ⩾30% (no. of patients scoring 2, 3 or 4, divided by the total number that completed the item), range of responses at least two points (1–3 or 2–4) and at least 33% of patients or HCPs prioritising the item.
Johnson C, Aaronson N, Blazeby J, Bottomley A, Fayers P, Koller M, et al. Guidelines for developing Questionnaire modules. Report 4th Ed. Brussels, 2011.
are that five of seven criteria should be met: mean score >1.5, prevalence ⩾30% or prevalence of scores 3 or 4 >50%, range >2 points, no floor/ceiling effect (responses in categories 3&4 or 1&2 >10%), no significant concerns expressed by patients (e.g. upsetting, ambiguous item), consistency across languages/cultures and at least 95% response to the item. However, items that meet four criteria may be retained, if patient interviews provide strong arguments for retaining them (e.g. emphasising the importance in a considerable number of interviews) and the module developers conclude that inclusion is clinically appropriate.
Johnson C, Aaronson N, Blazeby J, Bottomley A, Fayers P, Koller M, et al. Guidelines for developing Questionnaire modules. Report 4th Ed. Brussels, 2011.
The PASW 18 was used for all statistical analyses (SPSS Inc., Chicago, Il, United States of America).
3. Results
3.1 Phase 1, Generation of issues
The literature searches yielded 232 hits. Of 37 papers, 17 were specific studies assessing oral health. Manual hand searching of the reference lists yielded another two studies. Altogether, 31 relevant questionnaires were reviewed.
social function and QoL related to oral problems; 8 items.
Eighteen HCPs from Norway (n = 10), United Kingdom (UK) (n = 4) and Greece (n = 4) were interviewed. The selection of professionals was performed to cover a broad spectrum of experience in oral problems in cancer and the experts (male/female: 10/8) consisted of oncologists (n = 8), oncology nurses (n = 4), oral surgeons/dentists (n = 5) and one dental hygienist. Two items were deleted after the HCP interviews; one duplicate, and one that was regarded as being related to physicians’ decision making (‘dose-limiting effect of mouth-problems’).
The 83-item list was then used in interviews with 133 patients from Norway (n = 30), Greece (n = 30), UK (n = 15), Germany (n = 9), France (n = 27) and Netherlands (n = 22), representing different diagnoses and treatment phases, Table 2.
Table 2Characteristics of patient samples, phase 1 and 3.
Characteristics
Phase 1
Phase 3
N = 133 (%)
N = 178 (%)
Age, years
Median (range)
62.0 (22–88)
62.5 (21–85)
Gender
Male
57 (43)
86 (48)
Female
76 (57)
92 (52)
Country
France
27 (20)
–
Germany
9 (7)
36 (20)
Greece
30 (23)
30 (17)
Israel
–
18 (10)
Netherlands
22 (16)
25 (14)
Norway
30 (23)
30 (17)
Sweden
–
9 (5)
United Kingdom (UK)
15 (11)
30 (17)
Diagnosis
Breast
43 (32)
32 (18)
Head and neck
27 (20)
26 (15)
Lymphoma/leukaemia
18 (14)
21 (12)
Gastro-intestinal
15 (13)
36 (20)
Lung
10 (8)
10 (6)
Prostate
8 (6)
13 (7)
Myeloma
3 (2)
6 (3)
Urogenital
3 (2)
4 (2)
Gynaecological
2 (1)
23 (13)
Kidney
2 (1)
2 (1)
Other
2 (1)
5 (3)
Treatment
Surgery only
10 (8)
9 (5)
Radiotherapy only
8 (6)
3 (2)
Chemotherapy only
23 (17)
38 (21)
Surgery + radiotherapy
13 (10)
10 (6)
Surgery + chemotherapy
30 (22)
44 (24)
Surgery + chemotherapy + radiotherapy
29 (21)
54 (30)
Radiotherapy + chemotherapy
10 (8)
17 (9)
High dose chemotherapy and stem cell transplantation (HSCT)
Fifty-two items were deleted after the interviews, Fig. 1. No new issues were suggested, but reformatting of issues (dental care, social relations and information) yielded an additional 10 items. The 41 items and corresponding domains are listed in Table 3.
Fig. 1European Organisation for Research and Treatment of Cancer (EORTC) OH17, summary of module development. (a) No new issues, but reformatting resulted in additional items. (b) From the QLQ-H&N35 module.
Development of a European Organization for Research and Treatment of Cancer (EORTC) questionnaire module to be used in quality of life assessments in head and neck patients.
European Organisation for Research and Treatment of Cancer (EORTC) answer categories; 1; ‘not at all’, 2; ‘a little’, 3; ‘quite a bit’ and 4; ‘very much’.
a European Organisation for Research and Treatment of Cancer (EORTC) answer categories; 1; ‘not at all’, 2; ‘a little’, 3; ‘quite a bit’ and 4; ‘very much’.
b EORTC answer categories; 1; ‘very poor’, 2; ‘excellent’.
Development of a European Organization for Research and Treatment of Cancer (EORTC) questionnaire module to be used in quality of life assessments in head and neck patients.
The European Organization for Research and Treatment of Cancer breast cancer-specific quality-of-life questionnaire module: first results from a three-country field study.
3.2 Phase 2: Construction of the provisional questionnaire
The remaining 41 issues were formatted into questions within the EORTC format. Items that covered the content in full were available from the EORTC item bank for 15 items; 13 from the QLQ-H&N35,
Development of a European Organization for Research and Treatment of Cancer (EORTC) questionnaire module to be used in quality of life assessments in head and neck patients.
The European Organization for Research and Treatment of Cancer breast cancer-specific quality-of-life questionnaire module: first results from a three-country field study.
Development of a European Organization for Research and Treatment of Cancer (EORTC) questionnaire module to be used in quality of life assessments in head and neck patients.
requiring a translation of one or two words only. The remaining issues were constructed as there were no identical items in the item bank. Translations were performed according to EORTC guidelines. Specific questions in the pilot interviews revealed that most patients preferred dichotomous scales for the item about dental treatment and use of dentures and that the latter should be followed by a skip session. Thus, seven items (no. 27–30 and 34–36) were dichotomous, and item 29 and 30 were only to be answered for those wearing dentures (Table 3) in the provisional module. Two items (40 and 41) were formatted with the same 1–7 scale used in the last two items of the EORTC QLQ-C30.
The European Organization for Research and Treatment of Cancer QLQ-C30: a quality-of-life instrument for use in international clinical trials in oncology.
The European Organization for Research and Treatment of Cancer QLQ-C30: a quality-of-life instrument for use in international clinical trials in oncology.
were completed and interviews performed in 178 patients at nine centres in seven countries (Table 2). The majority (58%) had education beyond compulsory schooling, were living with others (83%) and had good performance status; mean Karnofsky 82 (SD13). Thirty-two percent had localised disease, 45% advanced while 41 patients (23%) were in the palliative phase of cancer. About one-third of the patients used dentures.
The mean score of the 32 module items with a 4-point categorical scale was 1.5 or above for 10 items. Compliance exceeded 95% for all but one item (36) and a two point range was found with all items except no. 33. No ceiling effect was found, but a floor effect was present with all items. For 13 items, at least 30% of respondents endorsed the symptom. All items, statistical results and patients’ comments were subject to round table discussions in the module development group.
Twenty-four items were deleted (Table 3) and 17 retained, resulting in a 17-item module; QLQ-OH17. The main reason for deletion was failure to meet the sufficient number of criteria for inclusion.
Johnson C, Aaronson N, Blazeby J, Bottomley A, Fayers P, Koller M, et al. Guidelines for developing Questionnaire modules. Report 4th Ed. Brussels, 2011.
Nine items were kept despite meeting less than five criteria (3, 5, 8, 12, 20, 31, 34, 37 and 38). Eight of these met four criteria, were judged as clinically relevant by the oncologists and dentists in the module development group, and the majority were emphasised as important by patients.
Johnson C, Aaronson N, Blazeby J, Bottomley A, Fayers P, Koller M, et al. Guidelines for developing Questionnaire modules. Report 4th Ed. Brussels, 2011.
Item no. 3 (bleeding gums) that met three criteria was retained, due to its high clinical importance in certain situations, and high ranking of importance by patients.
Most patients today are dentate, but many patients have dentures that necessitate special attention e.g. in relation to chemotherapy. Patients were asked if they preferred a dichotomous or 4-point scale for items related to use of dentures, and if a skip session should be inserted. This resulted in the reformatting of one dichotomous item about dentures (46) followed by an optional last question (47).
The mean scores from H&N patients were compared to patients with other cancer types. Significantly higher mean scores (p < .05) were found with 14 of the items; 4, 10, 11, 14, 15, 16, 20, 21, 22, 28, 29, 37, 40 and 41 in Table 3, indicating good criterion validity. Seven of these were retained; 10, 14, 15, 16, 20, 28 and 37, meeting five of seven inclusion criteria (37 met four) and were judged as clinically relevant also in patients with other cancers (mean score >1.5 for seven of these eight). No significantly different mean scores were found when comparing the different phases of treatment. No specific language problems were detected.
The provisional questionnaire employed two different time-frames; the conventional EORTC format ‘during the past week’; no. 1–33 and 37–41, Table 3 and ‘during your current disease or treatment, not only the past week’, as in the QLQ-INFO25.
Many patients preferred the longer time frame also for ‘worries about the future’, so this was changed. Additional issues (n = 24) suggested by patients were either covered by the EORTC QLQ-C30/OH17 (n = 19), or were regarded as too specific (details about candida, molar pain etc. n = 5), not tabulated.
The aggregation of single items into scales is recommended to facilitate the interpretation of results.
Johnson C, Aaronson N, Blazeby J, Bottomley A, Fayers P, Koller M, et al. Guidelines for developing Questionnaire modules. Report 4th Ed. Brussels, 2011.
Three multi-item scales were proposed in the QLQ-OH17, based on their content and clinical relevance; pain discomfort, xerostomia and eating. Cronbach’s alpha coefficient was calculated, including the multi-trait scaling matrix, yielding coefficients from .67 to .77 for the proposed scales indicating good internal consistency, Table 4. A fourth scale related to information was also suggested, consisting of two items. Cronbach’s alpha coefficient was not calculated for this scale as one of the items was dichotomous. Three single items were suggested; two on dentures and one about future worries.
Cronbach’s alpha was not calculated for the two information items that were retained (44 and 45), because one of these (no. 44) was a dichotomous question in phase 3.
a Cronbach’s alpha was not calculated for the two information items that were retained (44 and 45), because one of these (no. 44) was a dichotomous question in phase 3.
The QLQ-OH17-module is a questionnaire module assessing oral and dental problems that may impact on quality of life in cancer patients. It is intended for use together with the core questionnaire EORTC QLQ-C30. The module addresses issues that may be due to both acute and long-term side effects from cancer treatment that are often not routinely assessed in follow-up consultations.
Increased awareness of dental and oral complications may prevent the development of more serious problems that may impact on nutrition, social function and QoL. For example, chemotherapy often induces temporary salivary gland hypofunction and xerostomia. Saliva is important to maintain oral homeostasis and forms an integral part of taste perception while taste in turn is important for the saliva formation.
Thus loss or impairment of one function will influence the other. Furthermore, targeted interventions may be relatively simple at an early stage, in the form of saliva stimulants and supplements, management of clinical oral candidiasis e.g. plaque removal and caries prevention. These are prevalent problems in palliative care cancer patients,
but also frequent during different stages of cancer treatment.
It could be argued that the QLQ-OH17 has the form of a symptom checklist rather than a QoL questionnaire. We favour this, because thorough symptom assessment requires specific, detailed questions. Furthermore, issues related to oral and dental problems may not receive attention in regular follow-up consultations. However, the form is intended for use together with the EORTC QLQ-C30, and this, together with the three hypothesised scales (pain/discomfort, xerostomia and problems with eating) will address the multidimensional concept of QoL.
Thirty percent of the patients used dentures. Ill-fitting dentures may pose significant problems with negative consequences for QoL and functions, and were regarded as an important item to retain, by patients and the module developers. Because this only applies to a subset of patients, it was decided to keep this as a dichotomous screening item (46) as a question followed by a skip session.
Three of the hypothesised scales were constructed on the basis of clinical importance and supported by the correlation analyses, while the information scale now containing two items to be answered on the conventional four-point scale, will be tested in phase four. From a clinical point of view, some items could potentially load on more than one scale. However, it was decided that each item should be allocated to a single scale only.
Johnson C, Aaronson N, Blazeby J, Bottomley A, Fayers P, Koller M, et al. Guidelines for developing Questionnaire modules. Report 4th Ed. Brussels, 2011.
The study has shown that the QLQ-OH17 is relevant, acceptable and applicable to patients in different countries and language groups. The provisional questionnaire tested in phase 3 appeared to have good reliability, internal consistency and convergent validity. This is supported by the fact that no translation problems became apparent. The QLQ-OH17 contains eight items from the EORTC item bank.
Development of a European Organization for Research and Treatment of Cancer (EORTC) questionnaire module to be used in quality of life assessments in head and neck patients.
The European Organization for Research and Treatment of Cancer breast cancer-specific quality-of-life questionnaire module: first results from a three-country field study.
Overlapping items ensure compatibility with other modules, and permits use in different cancer types without necessitating patient completion of two or more modules..
The QLQ-OH17 has received wide attention and was recently translated into Italian. The module will now undergo international field-testing to further confirm aspects of reliability and validity, its cross-cultural applicability, the ability to discriminate between groups and its psychometric properties.
Conflict of interest statement
None declared.
Acknowledgements
This project was generously supported by Grant No. 002/2008 from the EORTC QLG group. The authors want to thank Kristin Bjordal, Norway, who gave valuable advice in the protocol writing, Margaret Kristensen who helped out with the initial literature searches, Triantafyllia Sarri and Tal Weissman who performed the translations and work in Greece and Israel, respectively. We express our gratitude to Juan Arraras and Colin Johnson (phase 1) and Juan Arraras, Pernille Jensen and Teresa Young (phase 3) for reviewing the module development reports.
Special thanks are also given to the study coordinators at the participating centres and the patients who took part in the study.
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The European Organization for Research and Treatment of Cancer QLQ-C30: a quality-of-life instrument for use in international clinical trials in oncology.
The performance status scale for head and neck cancer patients and the functional assessment of cancer therapy-head and neck scale. A study of utility and validity.
Matched case-control study of quality of life and xerostomia after intensity-modulated radiotherapy or standard radiotherapy for head-and-neck cancer: initial report.
Development of a European Organization for Research and Treatment of Cancer (EORTC) questionnaire module to be used in quality of life assessments in head and neck patients.
Johnson C, Aaronson N, Blazeby J, Bottomley A, Fayers P, Koller M, et al. Guidelines for developing Questionnaire modules. Report 4th Ed. Brussels, 2011.
The European Organization for Research and Treatment of Cancer breast cancer-specific quality-of-life questionnaire module: first results from a three-country field study.
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