Public Class Form1
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim list As New List(Of String)
        Dim i As Integer
 
        For i = 0 To ListBox1.Items.Count - 1
            list.Add(ListBox1.Items(i))
        Next i
 
        ListBox1.Items.Clear()
 
        For Each s As String In list.Distinct
            ListBox1.Items.Add(s)
        Next
 
    End Sub
End Class

    Public NotInheritable Class CombinationComparer : Implements IEqualityComparer(Of String)
 
        Public Shadows Function Equals(ByVal x As String, ByVal y As String) As Boolean _
        Implements IEqualityComparer(Of String).Equals
 
            ' (temporalmente) Ordeno de forma ascendente los números de una cadena de texto delimitada por comas;
            '
            ' e.g.:
            ' Una cadena de texto como "3, 1, 2" (con, o sin espacios en blanco), 
            ' se transformaría en "1,2,3" (sin espacios en blanco).
 
            x = String.Join(",", From value As String In x.Split({","c, " "c}, StringSplitOptions.RemoveEmptyEntries)
                                 Order By value Ascending)
 
            y = String.Join(",", From value As String In y.Split({","c, " "c}, StringSplitOptions.RemoveEmptyEntries)
                                 Order By value Ascending)
 
            #If DEBUG Then
                        Console.WriteLine(String.Format("x:{0}", x))
                        Console.WriteLine(String.Format("y:{0}", y))
                        Console.WriteLine()
            #End If
 
            Return (x = y)
 
        End Function
 
        Public Shadows Function GetHashCode(ByVal obj As String) As Integer _
        Implements IEqualityComparer(Of String).GetHashCode
 
            Return MyBase.GetHashCode()
 
        End Function
 
    End Class

Dim items As String() = Me.ListBox1.Items.Cast(Of String)().ToArray()
items = items.Distinct(New CombinationComparer).ToArray()
 
With Me.ListBox1
    .SuspendLayout()
    .Items.Clear()
    .Items.AddRange(items)
    .ResumeLayout()
End With