Patients in the experimental group will receive a behavioural treatment integrated within the concepts of operant conditioning. The purpose of Behavioural Graded Activity (BGA) is to increase the level of physical activity in the patient's daily lives in a time-contingent manner. On top of that, a healthy behaviour will be positively reinforced to consequently create a withdrawal of the attention towards pain behaviour, which is seen as an unreliable "alarm sign" in chronic pain patients. The implementation of BGA after PNE is described in the guideline reported by the International Association for the Study of Pain.

The content of the leaflet has a biomedical approach in explaining pain and providing information on the different pain medication classes. This leaflet is mostly available in waiting rooms of oncology centres and units of the Flemish part of Belgium.

Assessed by the Medoc TSA-II Neurosensory Analyzer.

Assessed by the digital algometer, the Medoc TSA-II Neurosensory Analyzer and a manual blood pressure cuff.

Assessed by a manual blood pressure cuff.

Assessed objectively by conditioned pain modulation paradigm. A manual blood pressure is the conditioned stimulus, and the digital algometer and the Medoc TSA-II Neurosensory Analyzer are testing stimuli.

Assessed objectively by temporal summation paradigm. Ten testing stimuli will be applied, and subjects will be asked to rate their pain intensity on the first, fifth and tenth stimulus by using the Visual Analogue Scale.

• Measured with the 'Douleur Neuropatique 4'
• The minimum and maximum values: 0, 10
• Higher score means a worse outcome
• A score of 4 or higher indicates neuropathic pain

• Measured with the 'Central Sensitization Index'
• The minimum and maximum values: 0, 100
• Higher score means a worse outcome
• A score of 40 or higher indicates the presence of central sensitization

• Measured with the 'International Physical Activity Questionnaire short form'
• Total physical activity in MET-min/week and time spent sitting

• Measured with the 'logbook'
• Subjects enrolled in the intervention arm will have to fill in the logbook on daily basis.

• Measured with the 'Pittsburgh Sleep Quality Index'
• The minimum and maximum values: 0, 21
• Higher score means a worse outcome
• A scores above 5 indicates poor global sleep quality

• Measured with the 'Insomnia Severity Index'
• The minimum and maximum values: 0, 28
• Higher score means a worse outcome
• A scores of 8 or higher indicates insomnia

• Measured with the 'Fatigue Severity Scale'
• The minimum and maximum values: 9, 63
• Higher score means a worse outcome

• Measured with the 'Pain Catastrophizing Scale'
• The minimum and maximum values: 0, 52
• Higher score means a worse outcome
• A scores of 30 or higher indicates pain catastrophizing thoughts

• Measured with the 'Injustice Experience Questionnaire'
• The minimum and maximum values: 0, 48
• Higher score means a worse outcome

• Measured with the 'the Brief Illness Perception Questionnaire'
• The minimum and maximum values: 0, 10
• Higher score means a worse outcome

• Measured with the 'Pain Vigilance and Awareness questionnaire'
• The minimum and maximum values: 0, 90
• Higher score means a worse outcome

• Measured with the 'Depression, Anxiety, Stress Scale'
• The minimum and maximum values: 0, 21
• Higher score means a worse outcome

• Measured with the 'Depression, Anxiety, Stress Scale'
• The minimum and maximum values: 0, 21
• Higher score means a worse outcome

• Measured with the 'Depression, Anxiety, Stress Scale'
• The minimum and maximum values: 0, 21
• Higher score means a worse outcome

Patient adherence for the treatment sessions will be calculated as the ratio of the number of treatment sessions that were actually carried out versus the number of prescribed sessions.

Compliance will be calculated as the ratio of the total training duration (recorded in the logbooks) versus the prescribed total training duration, multiplied by 100.

The diagnosis of Axillary Web Syndrome (AWS) will be made clinically.

• Scored on 5-point Likert scale (totally disagree, disagree, don't disagree/agree, agree, totally agree)
• The presence of rope-like cords in the axilla to the wrist is assessed by inspection and/or palpation.

Lymphedema will be clinically diagnosed:

The Stemmer sign is positive if the assessor is unable to pinch (between his/her thumb and index finger) the dorsal skin of proximal phalanx (second or third finger). A positive test confirms the presence of primary and secondary lymphedema of the arm(s).

Single circumference measurement will only be performed if unilateral lymphedema is suspected. The arm circumference will be measured by a nylon tape measure with an accuracy of 1mm. The tape measure will be placed around the arm without tightening the tape at 30cm above the styloid process. Lymphedema is present if there is at least a difference of 10% between both arms.

To assess arthralgia the assessor will ask the patient two questions: "Do you experience symmetrical pain in the left and right shoulders, elbows, wrists, fingers, hips, knees, ankles and/or toes?" and "Do you experience morning stiffness? And if so, for how many minutes?"

The scar tissue will be clinically scored. First, the assessor will inspect the affected (and painful) region for possible skin damage and will be looking for: wound disruption, hematoma (bruising), abscess (cavity filled with pus) and seroma (cavity filled with transparent liquid). Second, the he will inspect the presence of a possible inflammation process of the scar tissue and will be looking for signs such as: warmth, redness, etc. Third, he will assess the mobility of the scar. During this manual test, will be assessed whether the scar is moving relative to the underlying layers, which will be scored on a 5-point Likert scale with response possibilities: (totally disagree, disagree, don't disagree/agree, agree, totally agree).

• Measured with the 'Medical Consumption Questionnaire'
• 38 questions to quantify the direct medical costs of a patients' total medical consumption, encompassing additional diagnostics, consultations, surgery including stay in hospitals, physiotherapy, medication and aids prescribed by the general practitioner as well as medication and aids purchased by the patients themselves.

• Measured with the 'Productivity Cost Questionnaire'
• 20 questions to quantify the indirect costs outside health care but related to the disease (e.g. the costs due to absence of work and possible decreased productivity losses of paid and unpaid work).

• Measured with the 'EuroQol 5D instrument (EQ-5D-5L)'
• 5 dimensions scored on a 5-Likert scale and visual analogue scale (0 to 100)
• Higher score means a better outcome

Self-administered questions about: gender, ethnicity, age, nationality, weight, height, civil state, mutuality, educational level, year of the breast cancer diagnosis, received breast cancer treatments, lymphedema, medication, other treatments, menopausal, hot flashes.