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Progression of Type
In a given patient, the aggressiveness of PPB appears to progress over time when there is a recurrence. Also, as discussed above, PPB Types I, II, and III occur, on average, in progressively older cohorts of children (see Clinical Characteristics, Age at Diagnosis, above). Among literature and Registry cases are several well-documented examples of Type I disease recurring as Type II and thereafter as Type III disease. In fact, Type I disease almost never recurs as Type I. In no case has PPB Type “regression” (III to II or II to I) been seen.
However, in 2005-2007, several observations by Registry pathologists suggest that lung cysts which show similarities to Type I PPB and which occur in circumstances in which Type I PPB is highly suspect – may regress and not develop into frank malignancy. The special clinical circumstances in which these cases have been observed include siblings of PPB children or children with cystic nephroma and multiple lung cysts. The lung cysts are not typical of CCAM and show some features of Type I PPB, but do not show malignant cells or cambium layers. The Registry is eager to review cases in such situations [see Registry Publications Hill abstract 2007 Type I PPB].
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