Multiple sites ofmetastasis at recurrence is more commonly seen with the HER2 enriched subtypeof breast cancer. One study has shown a median number of sites involved atrecurrence being two 25. In the present study as well the HER2 subtype wasmost common among all to present with multiple sites of metastasis (50%). Inthe luminal A subtype as well the rate of multiple site metastasis was 50%although the total number of patients in was low in this subset of population. Thiswas closely followed by TNBC with 48% showing multiple site of metastasis. Inthe luminal B the rate of multiple sitemetastasis was lowest at 32% among all four subtypes. Although our studydescribes few differences in Indian population when compared to the existingliterature from the west, there are few limitations as well.
This studyidentified only those patients who presented with recurrence and doesn’t representthe exact incidence or the recurrence rate of each tumor subtype. Due to thepoor affordability, only two of our patients with HER-2 positive diseasereceived HER2 targeted therapy. There is a growingbody of evidence that indicates a lackof concordance in receptor status betweenprimary and recurrent/metastatic lesions (RML). The discordance rate of ER between primary breast cancer andcorresponding locoregional recurrences and distant metastases ranged from 12%to 30%, and for PR ranged from 18% to 40% 2-6. Discordance rates of8%–26% have been reported when HER2 of primary breast cancers and locoregionalor systemic recurrences were compared 7-10. The exact cause of thisdiscordance has not been confirmed.
Possible explanations include: pre-analytic andanalytic variability (eg. sampling errors, different techniques in processingand performing the tests) , intra-tumoral heterogeneity, clonal selection,variable ER-lineage differentiation of a putative disseminated breast cancerstem cell during the course of the disease, selective effect of previous treatments (adjuvant endocrine, chemotherapyand trastuzumab therapy) and, switch in tumor biology (eg. dedifferentiation)13. The discordance rate in our study was 21.9%, 32.3%, and 21.
8% for ER, PR,and HER2 respectively. This matches with the previous studies reported in theliterature, with a significant discordance rate for PR and HER2. The discordancerate for ER didn’t reach statistical significance. Studies have shown thatreceptor change from positive to negative being more common than from negativeto positive