import re
regex = r"(?<!\S)(\d+\.\d+x\d+\.\d+x\d+\.\d+) [cm]m(?!\S)"
test_str = "The study reveals a speculated nodule with pleural tagging at anterior basal segment of LLL, measured 1.9x1.4x2.0 cm in size"
print(re.findall(regex, test_str))
aW1wb3J0IHJlCgpyZWdleCA9IHIiKD88IVxTKShcZCtcLlxkK3hcZCtcLlxkK3hcZCtcLlxkKykgW2NtXW0oPyFcUykiCnRlc3Rfc3RyID0gIlRoZSBzdHVkeSByZXZlYWxzIGEgc3BlY3VsYXRlZCBub2R1bGUgd2l0aCBwbGV1cmFsIHRhZ2dpbmcgYXQgYW50ZXJpb3IgYmFzYWwgc2VnbWVudCBvZiBMTEwsIG1lYXN1cmVkIDEuOXgxLjR4Mi4wIGNtIGluIHNpemUiCgpwcmludChyZS5maW5kYWxsKHJlZ2V4LCB0ZXN0X3N0cikp