Occult Primary Breast Cancer

Three important conclusions are agreed upon regarding this clinical entity:
- Prognosis of occult primary breast cancer is the same or slightly better than women with classic stage IIA disease (T0, N1, M0)
- An exhaustive workup for the non-breast primary is usually not fruitful
- Treatment of the breast in some manner decreases the risk of local failure over time
Modified radical mastectomy has been the traditional surgical treatment for many years
Previously, the primary breast cancer was found in the mastectomy specimen:
- 40% to 80% of the time, but with the advent of much better mammography and ultrasound along with breast MRI, this rate is much lower now
However, what was true then and still holds today:
- Is that no treatment to the breast itself results in an unacceptably high local recurrence rate
An alternative to a modified radical mastectomy:
- Is complete ALND followed by whole-breast irradiation
Axillary dissection:
- Provides local control while also fine tuning staging
Theoretically the whole-breast radiation:
- Should control any subclinical disease in the breast not detected on imaging
Primary radiation to the breast, axilla, and supraclavicular area without any surgery of the breast or axilla:
- Results in higher local and regional recurrence compared to surgery and radiation combined
Axillary node dissection and whole-breast irradiation:
- Has been found to have equivalent survival as a modified radical mastectomy
A recent meta-analysis of 7 studies and more than 240 patients with occult primary breast cancers (0.3% to 0.8% of all breast cancers):
- Found 39% were treated with ALND and radiation while 47% had modified radical mastectomy and 15% had ALND alone
- With a mean follow-up of 5 years:
  - The study found no difference in local regional recurrence (12.7% vs 9.8%), distant metastasis (7.2% vs 12.7%), or mortality (9.5% vs 17.9%) between ALND and radiation vs modified radical mastectomy (all p>0.16)
ALND with radiation was superior to ALND alone in terms of local regional recurrence (12.7% vs 34.3%, p < 0.01) and trended towards improved survival but this was not statistically significant (P=0.09)
References:
- Barton SR, Smith IE, Kirby AM, Ashley S, Walsh G, Parton M. The role of ipsilateral breast radiotherapy in management of occult primary breast cancer presenting as axillary lymphadenopathy. Eur J Cancer. 2011;47:2099-2106. PMID: 21658935. http://www.ncbi.nlm.nih.gov/pubmed/21658935
- Dockery MB, Gray HK, Pierce EH. Surgical significance of isolated axillary adenopathy. Ann Surg. 1957;145:104-107. http://www.ncbi.nlm.nih.gov/pubmed/13395289
- Macedo FI, Eid JJ, Flynn J, Jacobs MJ, Mittal VK. Optimal surgical management for occult breast carcinoma: a meta-analysis. Ann Surg Oncol. 2016;23:1838-1844. https://www.ncbi.nlm.nih.gov/pubmed/26832884
- Rueth NM, Black DM, Limmer AR, et al. Breast conservation in the setting of contemporary multimodality treatment provides excellent outcomes for patients with occult primary breast cancer. Ann Surg Oncol. 2015;22:90-95. [epub ahead of print]. http://www.ncbi.nlm.nih.gov/pubmed/25249256
- Walker GV, Smith GL, Perkins GH, et al. Population-based analysis of occult primary breast cancer with axillary lymph node metastasis. Cancer. 2010;116:4000-4006. PMID: 20564117. http://www.ncbi.nlm.nih.gov/pubmed/20564117
- Woo SM, Son BH, Lee JW, et al. Survival outcomes of different treatment methods for the ipsilateral breast of occult breast cancer patients with axillary lymph node metastasis: a single center experience. J Breast Cancer. 2013;16:410-416. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3893343/