The mammosheres are the most aggressive type of breast cancer cells which exclusively had its own molecular profile including CCND2, FGF3, CD4, WNT1, KAT2A, NUMB, ACAN, COL2A1, TUBB3 ASCL2, FOXA2, ISL1, DTX1, and DVL. These genes could be considered as molecular markers for aggressiveness, metastasis, and resistance to treatment. The gene discussed is ISL1; the disease is breast cancer.