Mammary secretory carcinoma
[1] MSC usually affects women but in a significant percentage of cases also occurs in men and children.
MSCs typically develop as ductal breast tumors that have invaded the tissue around their ducts of origin, may have spread to nearby sentinel lymph nodes or axillary lymph nodes but have rarely metastasized (i.e. spread) to distant tissues.
The rare cases of MSC tumors that have metastasized to distal tissues have been treated with chemotherapy and radiation therapy but have shown little to no responses to these treatments.
[1] (In younger patients, these tumors more often occur beneath the areola, i.e. pigmented region around the breast's nipple.
[14]) In a subgroup of 99 patients on which there was sufficient information, average tumor sizes were 2.3 centimeters (cm.)
[5] In occasional cases, the cells in MSC tumors are arranged in a papillary (i.e. finger-like)[17] or tubular[14] pattern.
[15] The term “secretory” for MSC is in recognition that the tumor cells vacuoles and globules are secreted extracellularly to give the tissues their microcystic appearance.
[8] At least 2 cases of MSC had sarcoma-like malignant cells in portions of their tumors and a rapidly metastasizing disease.
[15] Conservative surgery or simple mastectomy with biopsy of sentinel lymph nodes has been recommended for patients with MSC tumors that have more favorable prognoses.
Since MSC tumors grow slowly, carry relatively good prognoses, and if metastasizing to distant tissues usually do so only 10 to 20 years after,[14] there is no strong evidence for the benefit of adjuvant chemotherapy and/or radiotherapy[4] A retrospective study of 190 patients with MSC that had not metastasized to distant tissue found that breast-conserving surgery plus radiotherapy gave significantly better survival times than simple mastectomy.
[1][14] The rare cases of MSC tumors that spread to distant tissues on their initial presentation or after prior treatment have been treated with various chemotherapy regimens.
[8][13][14] Recently, three individuals (two juvenile females and one 26 year old male) with ETV6-NTRK3 fusion gene-harboring MSC tumors that metastasized to distant tissues were treated with Larotrectinib, a drug which attacks the genetic abnormality underlying this disease.
The drug is an orally available selective NTRKi inhibitor that blocks the NTRK3 protein's tyrosine kinase activity.
[13][15][19] Larotrectinib therapy may improve the survival times in individuals with MSC tumors that have poorer prognoses.
