Invasive cancer

Excerpt

Breast screening detects a wide spectrum of breast cancer, ranging from microfocal low-grade ductal carcinoma in situ (DCIS) to large high-grade invasive cancer (Cowan et al., 1991; Klemi et al., 1992; Rajakariar et al., 1995). It has been proposed that detecting in situ cancer, particularly high-grade DCIS, would prevent the development of high-grade invasive cancer (Lampejo et al., 1994; Evans et al., 1997, 2001). It is well recognised that many low-grade, special invasive cancers are identified at screening (Cowan et al., 1991; Klemi et al., 1992; Porter et al., 1999). Such tumours have an excellent prognosis but may be so indolent that they would never have presented clinically or have threatened the life of the patients. It has been proposed alternatively that a proportion of these low-grade invasive tumours might de-differentiate over time into more aggressive, less well differentiated tumours (Tabár et al., 1999), although this was not found in another screening programme (Hakama et al., 1995). Identification and removal of such cancers when they are at a low-grade would avoid such progression. Detection of high-grade invasive cancers when they are small is clearly a means by which screening could reduce breast cancer mortality. In support of this possibility, it was shown in the two-county trial in Sweden that histological grade 3 invasive cancers detected when less than 10 mm have an excellent prognosis (Tabár et al., 1999), while it is widely recognised that large high-grade invasive cancers have a poor prognosis. In addition the presence of vascular invasion and lymph node metastasis, which are associated with development of metastatic disease, are rare in grade 3 tumours <10 mm, grade 2 tumours <10 mm and grade 1 tumours <20 mm, indicating that detecting tumours under a certain size should be beneficial (Evans et al., 2001). …