C50: Breast

The breast is one of the most commonly treated sites in radiation oncology. Therefore it helps to know the correct coding.


If a lesion has been specified as arising in a quadrant, use the appropriate code:

  • C50.2: Upper Inner Quadrant
  • C50.3: Lower Inner Quadrant
  • C50.4: Upper Outer Quadrant
  • C50.5: Lower Outer Quadrant

If a lesion arises between two quadrants, or is multicentric, use C50.8: Overlapping Lesion

Clock Face

Often lesions arise at 12, 3, 6 or 9 o'clock and are therefore not classifiable into a quadrant. In this case use C50.8. Specify the clock position if possible as it may come into use in future editions of ICD.

Other sites in breast

Lesions arising in the nipple are C50.0.
Lesions arising in the central breast are C50.1
Lesions arising from the axillary tail are C50.6.

Thoughts for improving breast cancer coding


I think that one of the greatest weaknesses of the ICD-10 system is the lack of laterality. C50.5 means a breast cancer of:

  • The left breast
  • The right breast
  • Both breasts
  • Breast, unknown side

The code could therefore be expanded by adding an additional symbol after the C50., eg C50.R.8 or alternatively C50.8.R which would mean an overlapping lesion of the right breast.

Bilateral Cancers

Some unfortunately women develop bilateral breast cancers. What should be coded for this? They are usually distinct malignancies and therefore have different sizes, location and histology. The options include:

  • C50.8: This is an overlapping lesion of the breast, which technically a bilateral tumour is. There is no way to split this from those tumours arising at 12, 3, 6 or 9 o'clock though which are also coded as C50.8.
  • Code each tumour separately. But if the patient is receiving a single course of treatment for both cancers, which one is the primary diagnosis? How do you indicate that the patient does have two breast cancers? This is especially troublesome given the lack of laterality coding described above.

ICD-O-3 would code two separate malignancies as C50.4 8500/3, C50.4 8500/3 but again lacks laterality.

My solution would be to include a special bilateral code "C50.7" (which is not currently used) or "C50.B" that would indicate that the patient has a bilateral tumour. The tumours could be separately coded and linked to the bilateral tumour diagnosis. This would allow for easy identification of these patients on reports and on medical record review.

12, 3, 6 and 9 o'clock tumours

The number of tumours arising between quadrants is reasonably significant (about 10-20% of cases). These are all lumped in to C50.8 "overlapping site". One option would be to add several codes to C50.8:

  • C50.80 - 12 o'clock lesion
  • C50.81 - 3 o'clock lesion
  • C50.82 - 6 o'clock lesion
  • C50.83 - 9 o'clock lesion
  • C50.88 - Overlapping lesion, not otherwise specified

Is this important? I think it is fairly important to separate the 3 o'clock medial right breast tumours from the 9 o'clock lesions if you wanted to look at, for instance, rates of IMC involvement.


Breast Anatomy

Breast Cancer Management