Rationale:To improve the definition of the target volume for radiotherapy of the chestwall after different types of mastectomy, the exact localization of regions at risk for a local recurrence should be known. However, there are currently insufficient data in literature showing where local recurrences occur after different types of mastectomy.

Objective: The primary objective of the proposed study is to determine whether the spatial, location of a breast cancer recurrence after mastectomy, differs for different types of mastectomy.

Study design: Retrospective study evaluating spatial location and site of recurrences after mastectomy.

Study population: The investigators aim to include all breast cancer patients treated with mastectomy in the Netherlands between 2003- 2008, and known to have experienced a local recurrence as the first site of failure.

Primary endpoint: Spatial location of local recurrence (e.g., primary tumour bed, scar, skin, subcutaneous, nipple, areola, pectoral muscles).

Rationale:To improve the definition of the target volume for radiotherapy of the chestwall after different types of mastectomy, the exact localization of regions at risk for a local recurrence should be known. However, there are currently insufficient data in literature showing where local recurrences occur after different types of mastectomy.

Objective: The primary objective of the proposed study is to determine whether the spatial, location of a breast cancer recurrence after mastectomy, differs for different types of mastectomy. Secondary objectives are to assess whether tumour characteristics (e.g., molecular subtypes, lymphangio/lymphovascular invasion) and treatment-related factors (e.g., PMRTwith or without bolus, radiation volumes, doses) influence the site of recurrence and spatial location.

Study design: Retrospective study evaluating spatial location and site of recurrences after mastectomy.

Study population: The investigators aim to include all breast cancer patients treated with mastectomy in the Netherlands between 2003- 2008, and known to have experienced a local recurrence as the first site of failure.

Primary endpoint: Primary endpoint: Spatial location of local recurrence (e.g., primary tumour bed, scar, skin, subcutaneous, nipple, areola, pectoral muscles).

Other study parameters: First descriptive statistics will be performed to investigate whether there is a relation between the localization of the recurrence and the type of mastectomy: modified radical mastectomy (MRM), skin-sparing mastectomy (SSM), nipple sparing mastectomy (NSM).

Inclusion Criteria:

• Age 18 years and more at the time of breast cancer diagnosis.
• Proven histology of first invasive breast cancer
• Mastectomy as a surgical procedure for breast cancer (regardless of perioperative treatment).
• Having a local recurrence, as primary event
• reast cancer diagnosis in the period 2003-2008.

Exclusion Criteria:

• Non-epithelial histology.
• Primary metastatic breast cancer.
• Mastectomy for breast cancer recurrence after earlier breast conserving therapy.
• Synchronous breast cancer.

We aim to include all breast cancer patients treated with mastectomy in the Netherlands between 2003- 2008, and known to have experienced a local or regional recurrence or distant metastases as the first site of failure.